YOSHINOBU NAKATANI
| Department of Computer and Network Engineering | Professor |
| Cluster I (Informatics and Computer Engineering) | Professor |
Researcher Information
Research Activity Information
Paper
- Reducing switching current with Gilbert damping constant in nanomagnets with perpendicular anisotropy under Dzyaloshinskii–Moriya interaction
Keisuke Yamada; Shun-ichi Takamatsu; Hiroki Asakawa; Yoshinobu Nakatani
Last, Applied Physics Express, IOP Publishing, 16, 11, 113001-113001, 01 Nov. 2023, Abstract
We report current-induced magnetization switching (jsw) with a nanosecond-duration pulse current (tp) in a perpendicularly magnetized nanomagnet under the Dzyaloshinskii–Moriya interaction (DMI) and investigate the effect of the Gilbert damping constant (α), tp, and DMI value (D) on jsw via micromagnetic simulations. When α is sufficiently small at tp = 1 ns, jsw for D = 1.0 erg cm−2 decreases by 42% compared to that for D = 0 erg cm−2. Further, jsw can be reduced under the DMI when α is small and tp is short, which is attributed to the twisted magnetization and increased initial magnetization angle.
Scientific journal - Magnetic octupole domain evolution and domain-wall structure in the noncollinear Weyl antiferromagnet Mn3Ge
Mingxing Wu; Kouta Kondou; Yoshinobu Nakatani; Taishi Chen; Hironari Isshiki; Tomoya Higo; Satoru Nakatsuji; Yoshichika Otani
APL Materials, AIP Publishing, 11, 8, 01 Aug. 2023, Peer-reviwed, Antiferromagnets with the intrinsic advantages of terahertz spin dynamics and negligible stray fields have been extensively studied for spintronic applications. In particular, spintronic research on antiferromagnets has expanded its focus from collinear to noncollinear Weyl antiferromagnets and discovered that Mn3X (X = Sn, Ge) produces substantial magneto-electric responses. Therefore, noncollinear antiferromagnets could be an ideal spintronic platform. Exploring the domain-wall features in Mn3X is, on the other hand, essential for spintronic device engineering. Here, we report an in-depth study on magnetic octupole domain evolution and domain-wall structure with a choice of Mn3Ge single crystal. Our magneto-optical imaging and the anomalous Hall measurements elucidate the nontrivial magnetic octupole domain nucleation, domain-wall propagation, and pinning behaviors. Moreover, combining the micromagnetic simulation, we reveal that Bloch- and Néel-like walls coexist in bulk with comparable sizes and energy densities. Our findings promote understanding the magnetic octupole domain-wall physics and designing domain-wall-based spintronic devices.
Scientific journal - Effects of structure, size and non-magnetic Cu layer thickness on magnetization switching behavior in Ni/Cu/M (M
Keisuke Yamada; Mayu Kikuchi; Anissa Binti Azizan; Yuuna Tsuchiya; Shota Ono; Yoshinobu Nakatani; Mutsuhiro Shima
Nano-Structures & Nano-Objects, Elsevier BV, 35, 101012-101012, Jul. 2023, Peer-reviwed
Scientific journal, English - Simulation of spin-orbit-torque switching of a perpendicular nanomagnet assisted by DMI
Joshiro Watanabe; Keisuke Yamada; Yoshinobu Nakatani
Last, IEEE Transactions on Magnetics, Institute of Electrical and Electronics Engineers (IEEE), 59, 11, 1-1, Jun. 2023, Peer-reviwed
Scientific journal, English - Elucidation of the mechanism for maintaining ultrafast domain wall mobility over a wide temperature range
S. Ranjbar; S. Kambe; S. Sumi; P. Thach; Y. Nakatani; K. Tanabe; H. Awano
MATERIALS ADVANCES, ROYAL SOC CHEMISTRY, 3, 18, 7028-7036, Sep. 2022, Peer-reviwed, To achieve a 20 Gbps data rate using the upcoming 5G communication standard, it is crucial to recognize a domain wall (DW) velocity (v(DW)) of 1200 m s(-1). We demonstrate a potential means of achieving the DW speed of 1200 m s(-1) at low current density in a wide temperature range from 270 to 350 K in Fe-rich GdFeCo magnetic wire. We show a significant relationship between the v(DW) and the pulse duration width, which corresponds to the Joule heating effect and the shape of the DW. Generally, if the current density is constant, the current-driven DW displacement is proportional to the pulse width, so the DW speed is also constant. We found that the v(DW) increases with the shortening of the applied pulse current width. However, the DW shape appears rounded in the case of long pulse duration width. Accordingly, the damping-like effective field and the Neel DW are not orthogonal to each other except in the wire center; as the efficiency of SOT decreases, the DW speed reduces. We also measured the Dzyaloshinskii-Moriya interaction (DMI) field for 3 ns 30 ns pulse duration widths. In the case of 30 ns, the DMI field was found halved in comparison to the 3 ns width. Generally, the DMI field is a material-specific parameter, and this difference is clarified by the shape of the DW driven by the current. Our findings on the fast and high thermal stability of DW motion at low current density in compensated ferrimagnetic material open new opportunities for high-speed spintronic devices.
Scientific journal, English - Adjacent Track Interference in Heat-Assisted Magnetic Recording
T. Kobayashi; Y. Nakatani; Y. Fujiwara
Journal of the Magnetics Society of Japan, 46, 3, 49-57, May 2022, We examine here the adjacent track interference (ATI) problem that arises when writing in an adjacent track for heat-assisted magnetic recording combined with shingled magnetic recording (shingled HAMR). For ATI, the bit error rate is a function of readout track width. We calculate the bit error rate and the minimum normalized readout field for various readout track widths. The factors affecting ATI are grain temperature and grain volume. We compare ATI and writing sensitivity for all combinations of 2 and 4 Tbpsi, and 6 and 9 grains/bit under the conditions of constant grain volume and constant grain height. For constant grain volume, 4 Tbpsi shingled HAMR is less advantageous than 2 Tbpsi shingled HAMR in terms of ATI due to the higher grain temperature caused by the smaller grain pitch. The grain number per bit must be lower and the grain height must be greater to be able to improve ATI for 4 Tbpsi shingled HAMR. We show there to be a loss of writing sensitivity for 4 Tbpsi shingled HAMR due to a statistical factor caused by the lower grain number per bit and the higher thermal stability factor resulting from the larger grain volume.
Scientific journal - Chirality-induced effective field in Pt/Co/MgO system with spatial anisotropy-modulation
T. Koyama; Y. Nakatani; D. Chiba
Applied Physics Letters, AIP Publishing, 120, 17, 172402-172402, 25 Apr. 2022, In a perpendicularly magnetized (PM) material with the interfacial Dzyaloshinskii–Moriya interaction (iDMI), a chirality-induced effective magnetic field (EMF) acts on a magnetic domain wall, which is a naturally formed in-plane magnetized (IM) region sandwiched by perpendicular (PM) regions. In this study, we artificially created a Pt/Co/MgO system with the regions exhibiting different anisotropy, that is, IM and PM regions, and the chirality-induced EMF at the PM/IM boundary was investigated using it. The EMF in the IM region was probed using magnetoresistance (MR) measurements. When the field was applied orthogonally to the wire, a unidirectional shift of the MR curve was observed, indicating that the EMF exists in the IM region. The dependence of the EMF on the width of the IM region suggests that the EMF acts dominantly on the magnetization near the PM/IM boundary. Moreover, the sign of the shift is reversed with reversing the PM direction. The sign and magnitude of the EMF observed in this study suggest that the EMF in the present system is caused by iDMI.
Scientific journal - Information Degradation during Archiving in Heat-Assisted Magnetic Recording
T. Kobayashi; Y. Nakatani; Y. Fujiwara
Journal of the Magnetics Society of Japan, 46, 1, 10-15, Jan. 2022, We examine the dependence of information stability on certain medium parameters, namely mean Curie temperature, grain height, and anisotropy constant ratio in 4 Tbpsi heat-assisted magnetic recording, for 10 years of archiving. We introduce a minimum normalized readout field H0 after 10 years of archiving and an information degradation rate R0 during 10 years of archiving. To interpret the results, we investigate whether there is a correlation between H0 or R0 and an effective thermal stability factor for 9 and 6 grains/bit. We find that there is a strong correlation since the anisotropy constant is much larger than the shape anisotropy. The H0 and R0 values are functions of the effective thermal stability factor and grain number, and are independent of grain number per bit. The effective thermal stability factor necessary for no information degradation is more than about 120. Furthermore, there is a weak correlation between the initial readout field or minimum readout field after 10 years of archiving and the effective thermal stability factor.
Scientific journal - Discrimination of skyrmion chirality via spin-orbit and -transfer torques for logic operation.
Yoshinobu Nakatani; Keisuke Yamada; Atsufumi Hirohata
Scientific reports, NATURE RESEARCH, 11, 1, 8415-8415, 16 Apr. 2021, True, Recently many works on magnetic memories and logic circuits, which use a magnetic skyrmion have been reported. Previously we micromagnetically simulated a method to switch a chirality of a magnetic skyrmion formed in a magnetic thin film by introducing a pulsed heat spot. In this paper, we propose a method to discriminate the chirality of a skyrmion in a branched nanowire by using spin-orbit torque (SOT) and spin-transfer torque (STT), and confirm the validity of the method by using simulation. The simulated results show that the motion changes depending on the chirality when additional SOT is applied on a skyrmion moving in a branch by STT. This method can be used as a fundamental building block for electrical detection in memory and logic devices using the chirality of skyrmions as a data bit in addition to the presence (and polarity) of the skyrmions as conventionally used, which can be lead to multiple-valued operation.
Scientific journal, English - Medium layer structure in three-dimensional heat-assisted magnetic recording
T. Kobayashi; Y. Nakatani; Y. Fujiwara
Journal of the Magnetics Society of Japan, 45, 2, 16-24, 01 Mar. 2021, We examine a medium layer structure in three-dimensional heat-assisted mag netic recording (3D HAMR) at 2 Tbpsi per layer (total density of 4 Tbpsi) where the medium consists of a high Curie temperature (HC) layer and a low Curie temperature (LC) layer. We perform a heat transfer simulation for 3D HAMR media including the isolation layer. To evaluate the grain error distribution, the expected value of the magnetization is calculated using the grain error probability. The error threshold and the time dependence of the bit error rate are discussed for 10 years of archiving. The information stability in the HC layer while writing in the LC layer is estimated using the temperature profile calculated by the heat transfer simulation. An LC (upper, namely, surface) / HC (lower) layer structure is compared with an HC (upper) / LC (lower) layer structure. The former is disadvantageous in relation to the medium surface temperature as regards writing in the HC layer. The latter may be disadvantageous in relation to the difference between the thermal gradients for HC and LC writing.
Scientific journal - Adjacent track interference in three-dimensional heat-assisted magnetic recording
T. Kobayashi; Y. Nakatani; Y. Fujiwara
Journal of the Magnetics Society of Japan, 45, 4, 79-85, 2021, We examine the adjacent track interference (ATI) problem that arises during three-dimensional heat-assisted magnetic recording (3D HAMR) at 2 Tbpsi per layer (total density of 4 Tbpsi) where the medium consists of a high Curie temperature (HC) layer and a low Curie temperature (LC) layer. To evaluate the grain error distribution, the expected magnetization value is calculated using the grain error probability. Prior to considering the ATI in 3D HAMR, we examine the ATI problem for conventional HAMR. Since the temperature of the LC layer in the adjacent tracks while writing in the HC layer (HC writing) exceeds the LC Curie temperature, HC writing will erase the data of the LC layer in the adjacent tracks. Therefore, we investigate 3D HAMR combined with shingled magnetic recording. The ATI in an LC (upper, namely, surface) / HC (lower) layer structure is compared with that in an HC / LC layer structure. The latter is disadvantageous in relation to ATI caused by the small thermal gradient in the LC layer.
Scientific journal - Determination of the Dzyaloshinskii-Moriya interaction using pattern recognition and machine learning
Masashi Kawaguchi; Kenji Tanabe; Keisuke Yamada; Takuya Sawa; Shun Hasegawa; Masamitsu Hayashi; Yoshinobu Nakatani
NPJ COMPUTATIONAL MATERIALS, NATURE RESEARCH, 7, 1, Jan. 2021, Machine learning is applied to a large number of modern devices that are essential in building an energy-efficient smart society. Audio and face recognition are among the most well-known technologies that make use of such artificial intelligence. In materials research, machine learning is adapted to predict materials with certain functionalities, an approach often referred to as materials informatics. Here, we show that machine learning can be used to extract material parameters from a single image obtained in experiments. The Dzyaloshinskii-Moriya (DM) interaction and the magnetic anisotropy distribution of thin-film heterostructures, parameters that are critical in developing next-generation storage class magnetic memory technologies, are estimated from a magnetic domain image. Micromagnetic simulation is used to generate thousands of random images for training and model validation. A convolutional neural network system is employed as the learning tool. The DM exchange constant of typical Co-based thin-film heterostructures is studied using the trained system: the estimated values are in good agreement with experiments. Moreover, we show that the system can independently determine the magnetic anisotropy distribution, demonstrating the potential of pattern recognition. This approach can considerably simplify experimental processes and broaden the scope of materials research.
Scientific journal, English - Control of current-induced skyrmion motion in ratchet-type skyrmion-based racetrack memory with a loop structure
Riki Yamaguchi; Keisuke Yamada; Yoshinobu Nakatani
JAPANESE JOURNAL OF APPLIED PHYSICS, IOP PUBLISHING LTD, 60, 1, Jan. 2021, We propose a method to realize a ratchet-type skyrmion-based racetrack memory with a loop structure using current and validate the proposed method using micromagnetic simulations. The proposed method utilizes the ratchet effect composed of a gradient with perpendicular magnetic anisotropy (PMA). The skyrmion moves circularly inside a track, which is composed of regions with various gradients of PMA. The results demonstrate that the recording density and operating frequency of the memory are approximately 40 Gbit inch(-2) and 42 MHz, respectively, when the diameter of the skyrmion is 28.1 nm.
Scientific journal, English - Electrical nucleation, displacement, and detection of antiferromagnetic domain walls in the chiral antiferromagnet Mn3Sn
Satoshi Sugimoto; Yoshinobu Nakatani; Yuta Yamane; Muhammad Ikhlas; Kouta Kondou; Motoi Kimata; Takahiro Tomita; Satoru Nakatsuji; Yoshichika Otani
Communications Physics, Springer Science and Business Media LLC, 3, 1, Dec. 2020, Peer-reviwed, Antiferromagnetic systems for application in spintronics are less developed that their ferromagnetic counterparts but offer the prospect of increased stability and speed in their magnetisation dynamics. Here, the authors investigate the electrical detection and displacement of antiferromagnetic domain walls in Mn3Sn single crystals.Antiferromagnets exhibiting distinctive responses to the electric and magnetic fields have attracted attention as breakthrough materials in spintronics. The current-induced Neel-order spin-orbit torque can manipulate the antiferromagnetic domain wall (AFDW) in a collinear CuMnAs owing to a lack of local inversion symmetry. Here, we demonstrate that the electrical nucleation, displacement, and detection of AFDWs are also possible in a noncollinear antiferromagnet, i.e., chiral Mn3Sn with local inversion symmetry. The asymmetric magnetoresistance measurements reveal that AFDWs align parallel to the kagome planes in the microfabricated wire. Numerical calculation shows these AFDWs consist of stepwise sub-micron size Bloch wall-like spin textures in which the octupole moment gradually rotates over three segments of domain walls. We further observed that the application of a pulse-current drives these octupole based AFDWs along the wire. Our findings could provide a guiding principle for engineering the AFDW structure in the chiral antiferromagnetic materials.
Scientific journal, English - Review on spintronics: Principles and device applications
Atsufumi Hirohata; Keisuke Yamada; Yoshinobu Nakatani; Ioan-Lucian Prejbeanu; Bernard Diény; Philipp Pirro; Burkard Hillebrands
Journal of Magnetism and Magnetic Materials, Elsevier BV, 509, 166711-166711, Sep. 2020, Peer-reviwed, Spintronics is one of the emerging fields for the next-generation nanoelectronic devices to reduce their power consumption and to increase their memory and processing capabilities. Such devices utilise the spin degree of freedom of electrons and/or holes, which can also interact with their orbital moments. In these devices, the spin polarisation is controlled either by magnetic layers used as spin-polarisers or analysers or via spin-orbit coupling. Spin waves can also be used to carry spin current. In this review, the fundamental physics of these phenomena is described first with respect to the spin generation methods as detailed in Sections 2 similar to 9. The recent development in their device applications then follows in Sections 10 and 11. Future perspectives are provided at the end.
Scientific journal, English - Controlling skyrmion motion in an angelfish-type racetrack memory by an AC magnetic field
Koudai Migita; Keisuke Yamada; Yoshinobu Nakatani
Applied Physics Express, IOP Publishing, 13, 7, 073003-073003, 01 Jul. 2020, Peer-reviwed, We propose a method to control the skyrmion motion in an angelfish-type racetrack composed of triangular regions of reduced magnetic anisotropy using an alternating current (AC) magnetic field with nanosecond ordering. The method is verified in micromagnetic simulations from which we found that the maximum velocity of the skyrmion is 11 m s(-1). Moreover, the direction the skyrmion moves can be reversed using the phase of the AC magnetic field. The results presented here offer a promising route to designing non-volatile memory and logic devices that utilize skyrmion motion.
Scientific journal, English - Thermally consistent SPICE model for magnetic tunnel junction with multi-layered structures via interlayer interaction
Ken Machida; Yasuyuki Kayama; Yoshinobu Nakatani
JAPANESE JOURNAL OF APPLIED PHYSICS, IOP PUBLISHING LTD, 59, 6, Jun. 2020, With the recent commercialization of large-scale integration products, which include embedded magnetoresistive random-access memory, the importance of simulation models for MRAM circuits (MRAM compact models) has been continuously increasing. To accurately reproduce the characteristics of MRAM devices, the physical mechanism of the MRAM device including temperature dependency should be precisely described. In this study, we propose an MRAM compact model based on the Landau-Lifshitz-Bloch equation according to a previously developed model, which was based on the Landau-Lifshitz-Gilbert equation. Furthermore, we extend the model by considering interlayer interactions for handling multi-layered magnetic tunnel junction (MTJ) structures. We infer that circuits including MRAM devices, which consist of multi-layered MTJ structures having unique thermal characteristics, can be designed through SPICE simulations.
Scientific journal, English - Reduction of the switching current in perpendicularly magnetized nanomagnets using an antiferromagnetic coupling structure
Keisuke Yamada; Keisuke Kubota; Yoshinobu Nakatani
Journal of Applied Physics, AIP Publishing, 127, 13, 133906-133906, 07 Apr. 2020, Peer-reviwed, This paper reports a current-induced magnetization switching with a nanosecond-scale pulse current in a nanomagnet using a perpendicularly magnetized synthetic antiferromagnetic coupling (p-AFC) structure. The results indicate that the magnetization switching current in the p-AFC structure is less than that in the single-nanomagnet structure with perpendicular anisotropy when the differences in thickness and saturation magnetization between the upper and lower layers of the p-AFC structure are small and the Gilbert damping constant is also small. The results also show that the p-AFC structure can reduce the switching current when the pulse duration is short and its structure is effective for a high-speed switching. The results of this study shall be useful in the design of spin-transfer torque random access memory. Published under license by AIP Publishing.
Scientific journal, English - Information Stability in Three-Dimensional Heat-Assisted Magnetic Recording
T. Kobayashi; Y. Nakatani; Y. Fujiwara
J. Magn. Soc. Jpn., 44, 2, 34-39, Mar. 2020, Peer-reviwed, The anisotropy constant ratio Ku / Kbulk necessary for information stability in three-dimensional heat-assisted magnetic recording (3D HAMR) of 2 Tbpsi (total density of 4 Tbpsi) is evaluated by employing a bit error rate calculation using grain error probability. The minimum Ku / Kbulk value of a high Curie temperature (HC) layer is limited by the information stability in the HC layer while writing in a low Curie temperature (LC) layer, and a high Ku / Kbulk is necessary for the HC layer. The minimum Ku / Kbulk value of the LC layer is limited by the information stability in the LC layer for 10 years of archiving, and a high Ku / Kbulk is also necessary for the LC layer since the anisotropy constant of the LC layer is intrinsically low at the storage temperature due to its low Curie temperature. At 9 grains/bit, the Ku / Kbulk values required for 3D HAMR are 0.85 and 0.86 for the HC and LC layers, respectively, taking account of certain variations, namely, standard deviations of 2 % for the Curie temperature and 15 % for the grain size.
Scientific journal, English - Media design for three-dimensional heat-assisted magnetic recording
T. Kobayashi; Y. Nakatani; Y. Fujiwara
Journal of the Magnetics Society of Japan, 44, 5, 122-128, 2020, We design media for three-dimensional heat-assisted magnetic recording at 2 Tbpsi (total density of 4 Tbpsi), taking account of heat transfer simulation, field calculation, and information stability in high Curie temperature (HC) and low Curie temperature (LC) layers. The medium surface temperature while writing in the HC layer, the thermal gradients while writing in the HC and LC layers, and the grain temperature difference between the HC and LC layers while writing in the LC layer are discussed by using a heat transfer simulation. The magnetic field strength as a function of distance from the layer surface for a single layer is discussed by employing a field calculation. The Curie temperatures of TLC and THC, and the grain heights of hLC and hHC in the LC and HC layers, respectively, are also discussed in terms of information stability during 10 years of archiving and writing in the LC layer. As a result, a media structure is decided whereby the upper, namely, the surface layer is an LC layer with TLC = 625 K and hLC = 4.5 nm, and the lower layer is an HC layer with THC = 750 K and hHC = 6.0 nm with an anisotropy constant ratio of 0.8.
Scientific journal - Information Stability in Heat-Assisted Magnetic Recording
T. Kobayashi; Y. Nakatani; Y. Fujiwara
J. Magn. Soc. Jpn., 43, 6, 114-119, Nov. 2019, Peer-reviwed, The thermal stability factor Kum Vm/kT and the anisotropy constant ratio Ku/Kbulk necessary for 10 years of archiving in heat-assisted magnetic recording of 2 Tbpsi are evaluated by employing a bit error rate calculation using a grain error probability P. Although the attempt frequency f0 in P is a function of the Gilbert damping constant, the Curie temperature, Ku/Kbulk, the grain volume, and temperature, f0 can be treated as a constant. The Gilbert damping constant and the Curie temperature variation are parameters with little impact. On the other hand, the grain size variation, the grain number per bit n, the mean Curie temperature Tcm, and the storage temperature T are parameters with a strong impact on bit error rate. Although Kum Vm/kT decreases as n increases due to a statistical problem, a larger Ku/Kbulk is necessary as n increases due to a smaller grain size. A larger Ku/Kbulk is also necessary as Tcm decreases. The bit error rate increases rapidly as T increases.
Scientific journal, English - Switching of Skyrmion chirality by local heating
Y. Nakatani; K. Yamada; A. Hirohata
Scientific Reports, NATURE PUBLISHING GROUP, 9, 1, 13475-13475, Sep. 2019, Peer-reviwed, True, Magnetic Skyrmions are energetically stable entities formed in a ferromagnet with a diameter of typically below 100 nm and are easily displaceable using an electrical current of 102 A/cm2, resulting the Skyrmions to be more advantageous than domain walls for spintronic memory applications. Here, we demonstrated switching of a chirality of magnetic Skyrmions formed in magnetic thin films by introducing a pulsed heat spot using micromagnetic simulation. Skyrmions are found to expand with a pulsed heat spot, which induces the magnetic moments surrounding the Skyrmion to rotate by this expansion, followed by the chirality switching of the Skyrmion. Such simple controllability can be used as a fundamental building block for memory and logic devices using the chirality of Skyrmions as a data bit.
Scientific journal, English - Voltage-controlled magnetic skyrmions in magnetic tunnel junctions
Shinya Kasai; Satoshi Sugimoto; Yoshinobu Nakatani; Ryo Ishikawa; Yukiko K. Takahashi
APPLIED PHYSICS EXPRESS, IOP PUBLISHING LTD, 12, 8, Aug. 2019, We investigated the fully electrical manipulation of magnetic skyrmions in combination with magnetic tunnel junctions. The high output voltage due to the tunneling magnetoresistance effect allows us to detect the single skyrmion, and its size can be identified around 220 nm in diameter. We also demonstrate skyrmion creation and annihilation by applying nano-second pulsed voltage, which offers the fully electrical memory function based on the magnetic skyrmion. (C) 2019 The Japan Society of Applied Physics
Scientific journal, English - Impact of Curie Temperature Variation on Bit Error Rate in Heat-Assisted Magnetic Recording
T. Kobayashi; Y. Nakatani; Y. Fujiwara
J. Magn. Soc. Jpn., 43, 4, 70-78, Jul. 2019, Peer-reviwed, The Curie temperature Tc variation problem in heat-assisted magnetic recording is discussed. We describe the physical implication of the Tc variation problem, and provide ways of improving the writing property by employing our simplified model calculation. The bit error rates for mean Curie temperatures of 600 and 700 K are examined. The Tc variation increases both write-error (WE) and erasure-after-write (EAW). The main related calculation parameters are the grain column number in one bit and the thermal gradient for the down-track direction. Increasing the grain column number is effective in reducing WE and EAW caused by the Tc variation. Furthermore, increasing the thermal gradient is necessary since EAW is high. Although a higher writing field of 12 to 14 kOe is necessary, a bit error rate less than 10-3 can be achieved for recording densities of 4 or 2 Tbpsi under the conditions used in this study even though the standard deviation of the Curie temperature is 4 %.
Scientific journal, English - Current-Induced Modulation of the Interfacial Dzyaloshinskii-Moriya Interaction.
Naoaki Kato; Masashi Kawaguchi; Yong-Chang Lau; Toru Kikuchi; Yoshinobu Nakatani; Masamitsu Hayashi
Physical review letters, AMER PHYSICAL SOC, 122, 25, 257205-257205, 28 Jun. 2019, True, The Dzyaloshinskii-Moriya (DM) interaction is an antisymmetric exchange interaction that is responsible for the emergence of chiral magnetism. The origin of the DM interaction, however, remains to be identified albeit the large number of studies reported on related effects. It has been recently suggested that the DM interaction is equivalent to an equilibrium spin current density originating from spin-orbit coupling, an effect referred to as the spin Doppler effect. The model predicts that the DM interaction can be controlled by spin current injected externally. Here we show that the DM exchange constant (D) in W/CoFeB-based heterostructures can be modulated with external current passed along the film plane. At higher current, D decreases with increasing current, which we infer is partly due to the adiabatic spin transfer torque. At lower current, D increases linearly with current regardless of the polarity of current flow. The rate of increase in D with the current density agrees with that predicted by the model based on the spin Doppler effect. These results imply that the DM interaction at the heavy-metal-ferromagnetic-metal interface partly originates from an equilibrium interface spin (polarized) current which can be modulated externally.
Scientific journal, English - Critical current formula of perpendicularly magnetized magnetic random access memory revisited
Taniguchi Tomohiro; Yamada Keisuke; Nakatani Yoshinobu
JAPANESE JOURNAL OF APPLIED PHYSICS, IOP PUBLISHING LTD, 58, 5, 01 May 2019, Peer-reviwed, A theoretical formula of the current necessary to reverse a perpendicular magnetization by the spin torque effect is derived by solving the Landau-Lifshitz-Gilbert equation. Our formula reproduces the critical current formulas in previous works under several limiting conditions such as an infinite pulse duration of current and low damping. On the other hand, our formula gives a different estimation of the critical current when the pulse duration and/or damping are finite. The comparison with numerical simulation confirms that the derived formula provides a highly accurate estimation of the critical current for a wide range of pulse durations and damping constants. (C) 2019 The Japan Society of Applied Physics
Scientific journal, English - Electric field control of magnetic domain wall motion via modulation of the Dzyaloshinskii-Moriya interaction
Tomohiro Koyama; Yoshinobu Nakatani; Junichi Ieda; Daichi Chiba
Science Advances, AMER ASSOC ADVANCEMENT SCIENCE, 4, 12, eaav0265, Dec. 2018, True, Copyright © 2018 The Authors. We show that the electric field (EF) can control the domain wall (DW) velocity in a Pt/Co/Pd asymmetric structure. With the application of a gate voltage, a substantial change in DW velocity up to 50 m/s is observed, which is much greater than that observed in previous studies. Moreover, modulation of a DW velocity exceeding 100 m/s is demonstrated in this study. An EF-induced change in the interfacial Dzyaloshinskii-Moriya interaction (DMI) up to several percent is found to be the origin of the velocity modulation. The DMI-mediated velocity change shown here is a fundamentally different mechanism from that caused by EF-induced anisotropy modulation. Our results will pave the way for the electrical manipulation of spin structures and dynamics via DMI control, which can enhance the performance of spintronic devices.
Scientific journal, English - Understanding Signal-to-Noise Ratio in Heat-Assisted Magnetic Recording
T. Kobayashi; Y. Nakatani; Y. Fujiwara
J. Magn. Soc. Jpn., 42, 6, 127-137, Nov. 2018, Peer-reviwed
Scientific journal, English - Magnetic domain wall motion in anti-ferromagnetic nanowires induced by sloped electric field
K. Yamada; K. Kubota; Y. Nakatani
Appl. Phys. Express, IOP PUBLISHING LTD, 11, 11, 113001, 2018, Peer-reviwed, Micromagnetic simulations are performed to analyze the sloped electric field (SEF)-driven motion of a magnetic domain wall (DW) in an anti-ferromagnetic (AFM) nanowire. Results show that the DW is moved by the SEF regardless of the absence of the Dzyaloshinskii-Moriya interaction (DMI). The DW velocity is independent of the DMI but is found to be proportional to the modulation ratio of the SEF, and the DW velocity is shown to reach 1 km/s. The DW motion is caused by the Neel field, which is the effective magnetic field generated in each magnetic sublattice by the SEF. (C) 2018 The Japan Society of Applied Physics
Scientific journal, English - Writing Field Sensitivity in Heat-Assisted Magnetic Recording
T. Kobayashi; Y. Nakatani; Y. Fujiwara
J. Magn. Soc. Jpn., 42, pp. 110-118, 2018, Peer-reviwed - Domain-wall resistance in CoFeB-based heterostructures with interface Dzyaloshinski-Moriya interaction
Y. Ishikuro; M, Kawaguchi; Y.-C. Lau; Y. Nakatani; M. Hayashi
Appl. Phys. Express, IOP PUBLISHING LTD, 11, 7, 73001, 2018, Peer-reviwed, We studied the domain-wall resistance in W/Ta/CoFeB/MgO heterostructures. The Ta layer thickness was varied to control the type of domain walls (DWs) via changes in the interfacial Dzyaloshinskii-Moriya interaction. The domain-wall resistance was nearly constant with changes in the Ta layer thickness. The anisotropic magnetoresistance, spin Hall magnetoresistance, and anomalous Hall effect contributed to the domain-wall resistance of the thick-Ta layer films. However, a discrepancy remains for the thin-Ta layer films, wherein chiral Neel-like DWs were observed. These results show the difficulty of studying the domain-wall type via resistance measurements. (C) 2018 The Japan Society of Applied Physics
Scientific journal, English - Writing Field Amplitude in Heat-Assisted Magnetic Recording
T. Kobayashi; Y. Nakatani; K. Enomoto; Y. Fujiwara
J. Magn. Soc. Jpn., 42, pp. 15-19, 2018, Peer-reviwed - Numerical Study on a Novel Curie Temperature Controlled Hybrid Thermo-Magnetic Structure for Magnetic Random Access Memories
Ken Machida; Yoshiaki Sonobe; Yoshinobu Nakatani
IEEE TRANSACTIONS ON MAGNETICS, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 53, 11, article number 2002205, Nov. 2017, Peer-reviwed, High thermal stability, a fast switching time, and a low switching current are key characteristics of merit for realizing gigabit-class magnetic random access memory (MRAM). Especially, the switching current needs to be reduced significantly for creating high-density MRAM. In order to realize these necessary features, a number of magnetic tunnel junction (MTJ) structures have been proposed. A previous study of ours led to the proposal of a novel Curie-temperature-controlled hybrid thermo-magnetic structure for MRAM, for the purpose of improving these advantageous properties. This paper presents an analysis of the switching time and switching current by using micromagnetic simulation techniques for comparing our structures with various MTJ structures that have been proposed recently. We confirm that our novel structure can improve the switching characteristics of MRAM. The results of our analysis revealed that a 44% lower switching current and a 32% faster switching time can be achieved compared with the conventional structure.
Scientific journal, English - Examination of the stability of skyrmion structures in perpendicularly-magnetized Co/Ni films
Keisuke Yamada; Shigeru Hozumi; Yoshinobu Nakatani
JAPANESE JOURNAL OF APPLIED PHYSICS, IOP PUBLISHING LTD, 56, 5, 50309, May 2017, Peer-reviwed, The conditions of skyrmion structures in Co/Ni films with perpendicular anisotropy and the Dzyaloshinskii-Moriya interaction (DMI) are reported using micromagnetic simulations. It was found that skyrmion structures existing around the DMI constant D similar to 1.0 erg/cm(2) exhibit a perpendicular magnetic anisotropy (K-u) in the range of 4.4 <= K-u <= 6.0 Merg/cm(3). This K-u range is almost identical to the range obtained using analytical equations. However, skyrmion-annihilating conditions were obtained for simulations at small D values. Moreover, the D value required for skyrmion structures suitable for memory applications was (D-c - 0.1) <= D <= D-c erg/cm(2) from the magnetic energy calculations. (C) 2017 The Japan Society of Applied Physics
Scientific journal, English - Energy-efficient writing scheme for magnetic domain-wall motion memory
Kab-Jin Kim; Yoko Yoshimura; Woo Seung Ham; Rick Ernst; Yuushou Hirata; Tian Li; Sanghoon Kim; Takahiro Moriyama; Yoshinobu Nakatani; Teruo Ono
APPLIED PHYSICS EXPRESS, IOP PUBLISHING LTD, 10, 4, 43002, Apr. 2017, Peer-reviwed, We present an energy-efficient magnetic domain-writing scheme for domain wall (DW) motion-based memory devices. A cross-shaped nanowire is employed to inject a domain into the nanowire through current-induced DW propagation. The energy required for injecting the magnetic domain is more than one order of magnitude lower than that for the conventional field-based writing scheme. The proposed scheme is beneficial for device miniaturization because the threshold current for DW propagation scales with the device size, which cannot be achieved in the conventional field-based technique. (C) 2017 The Japan Society of Applied Physics
Scientific journal, English - Impact of Damping Constant on Bit Error Rate in Heat-Assisted Magnetic Recording
T. Kobayashi; Y. Nakatani; F. Inukai; K. Enomoto; Y. Fujiwara
J. Magn. Soc. Jpn., The Magnetics Society of Japan, 41, 3, pp. 52-57-57, 2017, Peer-reviwed,We calculate the writing field dependence of the bit error rate for Gilbert damping constants of 0.1 and 0.01 in heat-assisted magnetic recording (HAMR) using a new model calculation. The attempt period used in the new model calculation is considered in detail. The writing properties are examined for various thermal gradients, linear velocities, and anisotropy constants. When the damping constant is equal to 0.1, write-error is smaller, and erasure-after-write is larger than that for 0.01 since the attempt period is short. The physical implication of the results is discussed. We also compare the results of the new model calculation and the conventionally used micromagnetic calculation. The overall tendencies of the results are the same. Therefore, the outline of the impact of the damping constant on the bit error rate in HAMR can be understood by the grain magnetization reversal probability and the attempt period used in the new model calculation.
English - Magnetic domain wall motion in Co/Ni nanowires induced by a sloped electric field
Keisuke Yamada; Soh Murayama; Yoshinobu Nakatani
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 108, 20, 202405, May 2016, Peer-reviwed, We report the sloped-electric-field (SEF)-driven motion of a magnetic domain wall (DW) in a Co/Ni nanowire with a perpendicular anisotropy using micromagnetic simulations. The results show that the DW velocity increases in proportion to the modulation ratio of the SEF, and rapidly decreases above a threshold ratio of SEF (i.e., the breakdown). We derived the analytical equation of the effective magnetic field caused by the SEF, and show the resultant DW velocity. Also, we found that the maximum DW velocity is three times faster when the Dzyaloshinskii-Moriya interaction is 0.06 erg/cm(2). The results presented here offer a promising route for the design of non-volatile memory and logic devices using only the electric-field. Published by AIP Publishing.
Scientific journal, English - Depinning field of domain walls with a misaligned grain boundary in iron-based soft magnets
Keisuke Yamada; Shota Irie; Soh Murayama; Yoshinobu Nakatani
APPLIED PHYSICS EXPRESS, IOP PUBLISHING LTD, 9, 5, 53003, May 2016, Peer-reviwed, We report on the domain wall (DW) depinning in an iron-based soft magnet with a misaligned grain boundary (GB) using micromagnetic simulations. The results show that the depinning magnetic field decreases with increasing roughness of the misaligned GB. This effect can be explained from the ratio of the overlapping areas of the GB to the DW when the DW is depinned from the GB. The results presented here offer a promising route to the design of soft magnets to decrease coercive force. (C) 2016 The Japan Society of Applied Physics
Scientific journal, English - Electric field control of Skyrmions in magnetic nanodisks
Y. Nakatani; M. Hayashi; S. Kanai; S. Fukami; H. Ohno
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 108, 15, 152403, Apr. 2016, Peer-reviwed, The control of magnetic Skyrmions confined in a nanometer scale disk using electric field pulses is studied by micromagnetic simulation. A stable Skyrmion can be created and annihilated by an electric field pulse depending on the polarity of the electric field. Moreover, the core direction of the Skyrmion can be switched using the same electric field pulses. Such creation and annihilation of Skyrmions, and its core switching do not require any magnetic field and precise control of the pulse length. This unconventional manipulation of magnetic texture using electric field pulses allows a robust way of controlling magnetic Skyrmions in nanodiscs, a path toward building ultralow power memory devices. (C) 2016 AIP Publishing LLC.
Scientific journal, English - Observation of asymmetry in domain wall velocity under transverse magnetic field
K. -J. Kim; Y. Yoshimura; T. Okuno; T. Moriyama; S. -W. Lee; K. -J. Lee; Y. Nakatani; T. Ono
APL MATERIALS, AMER INST PHYSICS, 4, 3, 32504, Mar. 2016, Peer-reviwed, The dynamics of a magnetic domain wall (DW) under a transverse magnetic field H-y are investigated in two-dimensional (2D) Co/Ni microstrips, where an interfacial Dzyaloshinskii-Moriya interaction (DMI) exists with DMI vector D lying in +y direction. The DW velocity exhibits asymmetric behavior for +/- H-y; that is, the DW velocity becomes faster when H-y is applied antiparallel to D. The key experimental results are reproduced in a 2D micromagnetic simulation, which reveals that the interfacial DMI suppresses the periodic change of the average DW angle phi even above the Walker breakdown and that H-y changes phi, resulting in a velocity asymmetry. This suggests that the 2D DW motion, despite its microscopic complexity, simply depends on the average angle of the DW and thus can be described using a one-dimensional soliton model. These findings provide insight into the magnetic DW dynamics in 2D systems, which are important for emerging spin-orbitronic applications. (C) 2016 Author(s).
Scientific journal, English - Soliton-like magnetic domain wall motion induced by the interfacial Dzyaloshinskii-Moriya interaction
Yoko Yoshimura; Kab-Jin Kim; Takuya Taniguchi; Takayuki Tono; Kohei Ueda; Ryo Hiramatsu; Takahiro Moriyama; Keisuke Yamada; Yoshinobu Nakatani; Teruo Ono
NATURE PHYSICS, NATURE PUBLISHING GROUP, 12, 2, 157-+, Feb. 2016, Peer-reviwed, Topological defects such as magnetic solitons, vortices and skyrmions have started to play an important role in modern magnetism because of their extraordinary stability(1), which can be exploited in the production of memory devices. Recently, a type of antisymmetric exchange interaction, namely the Dzyaloshinskii-Moriya interaction (DMI; refs 2,3), has been uncovered and found to influence the formation of topological defects(4-7). Exploring how the DMI affects the dynamics of topological defects is therefore an important task. Here we investigate the dynamics of the magnetic domain wall (DW) under a DMI by developing a real time DW detection scheme. For a weak DMI, the DW velocity increases with the external field and reaches a peak velocity at a threshold field, beyond which it abruptly decreases. For a strong DMI, on the other hand, the velocity reduction is completely suppressed and the peak velocity is maintained constant even far above the threshold field. Such a distinct trend of the velocity can be explained in terms of a magnetic soliton, the topology of which is protected during its motion. Our results therefore shed light on the physics of dynamic topological defects, which paves the way for future work in topology-based memory applications.
Scientific journal, English - Reducing the switching current with a Gilbert damping constant in nanomagnets with perpendicular anisotropy (vol 106, 042402, 2015)
Keisuke Yamada; Kiyoaki Oomaru; Satoshi Nakamura; Tomonori Sato; Yoshinobu Nakatani
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 108, 5, Feb. 2016, Peer-reviwed
English - Magnetization switching by current and microwaves
Tomohiro Taniguchi; Daisuke Saida; Yoshinobu Nakatani; Hitoshi Kubota
PHYSICAL REVIEW B, AMER PHYSICAL SOC, 93, 1, 14430, Jan. 2016, Peer-reviwed, We propose a theoretical model of magnetization switching in a ferromagnetic multilayer by both electric current and microwaves. The electric current gives a spin transfer torque on the magnetization, while the microwaves induce a precession of the magnetization around the initial state. Based on numerical simulation of the Landau-Lifshitz-Gilbert (LLG) equation, it is found that the switching current is significantly reduced compared with the switching caused solely by the spin transfer torque when the microwave frequency is in a certain range. We develop a theory of switching from the LLG equation averaged over a constant energy curve. It was found that the switching current should be classified into four regions, depending on the values of the microwave frequency. Based on the analysis, we derive an analytical formula of the optimized frequency minimizing the switching current, which is smaller than the ferromagnetic resonance frequency. We also derive an analytical formula of the minimized switching current. Both the optimized frequency and the minimized switching current decrease with increasing the amplitude of the microwave field. The results will be useful to achieve high thermal stability and low switching current in spin torque systems simultaneously.
Scientific journal, English - 19aAU-8 Soliton-like magnetic domain wall motion induced by the interfacial Dzyaloshinskii-Moriya interaction
Yoshimura Yoko; Kim Kab-Jin; Taniguchi Takuya; Tono Takayuki; Ueda Kohei; Hiramatsu Ryo; Moriyama Takahiro; Yamada Keisuke; Nakatani Yoshinobu; Ono Teruo
Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS), 71, 1003-1003, 2016
Japanese - 19pPSB-53 Computer simulation of domain wall motion induced by a slope electric field and DMI
Murayama Soh; Yamada Keisuke; Nakatani Yoshinobu
Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS), 71, 1179-1179, 2016
Japanese - 19pPSB-51 Effect of the Gilbert damping constant of the switching current in Exchange-coupled composite type Spin-RAM
Takizawa Ryoto; Yamada Keisuke; Nakatani Yoshinobu
Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS), 71, 1177-1177, 2016
Japanese - 19pPSB-52 Effect of Gilbert damping constant on the domain wall pinning in permanent magnets
Kitajima Akimitsu; Yamada Keisuke; Nakatani Yoshinobu
Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS), 71, 1178-1178, 2016
Japanese - Excitation of magnetic domain wall velocity in (Co/Ni) nanowires induced by blocking the motion of vertical Bloch lines
Keisuke Yamada; Yoshinobu Nakatani
APPLIED PHYSICS EXPRESS, IOP PUBLISHING LTD, 8, 9, 93004, Sep. 2015, Peer-reviwed, We study the high-field-driven motion of a magnetic domain wall (DW) in a (Co/Ni) nanowire under the Dzyaloshinskii-Moriya interaction (DMI) by using micromagnetic simulations. The results show that the DW velocity above the Walker field (H-w) changes in response to not only the DMI strength but also the width of the nanowire. The DW velocity shows a re-increment depending on the magnetic field and reaches several hundred m/s, despite high-field regions above H-w. In the re-increment, the DW moves while maintaining its structure because the motion of vertical Bloch lines is blocked by the bending region of the DW. (C) 2015 The Japan Society of Applied Physics
Scientific journal, English - Precise control of magnetic domain wall displacement by a nanosecond current pulse in Co/Ni nanowires
Takuya Taniguchi; Kab-Jin Kim; Takayuki Tono; Takahiro Moriyama; Yoshinobu Nakatani; Teruo Ono
APPLIED PHYSICS EXPRESS, IOP PUBLISHING LTD, 8, 7, 73008, Jul. 2015, Peer-reviwed, Magnetic domain wall (DW) motion induced by nanosecond current pulses is investigated in Co/Ni nanowires where the DW motion is driven by either adiabatic spin transfer torque (STT) or spin Hall torque (SHT). The DW displacement, including transient displacement and steady-state displacement, is found to be linearly related to the current pulse duration for both current-induced torques. The transient displacement is found to be less than 10% of the DW displacement. This result implies that the DW position can be controlled by tuning the duration of the current pulse, which enables a robust operation of racetrack memory. (C) 2015 The Japan Society of Applied Physics
Scientific journal, English - Localized precessional mode of domain wall controlled by magnetic field and dc current
Ryo Hiramatsu; Kab-Jin Kim; Takuya Taniguchi; Takayuki Tono; Takahiro Moriyama; Shunsuke Fukami; Michihiko Yamanouchi; Hideo Ohno; Yoshinobu Nakatani; Teruo Ono
APPLIED PHYSICS EXPRESS, IOP PUBLISHING LTD, 8, 2, 23003, Feb. 2015, Peer-reviwed, We present evidence of a localized magnetic domain-wall (DW) oscillator in Co/Ni nanowires. It is found that a DW is localized by the simultaneous application of a high magnetic field larger than the depinning field and a dc current smaller than the threshold current. A one-dimensional model and micromagnetic simulation reveal that the localized DW is in a precessional mode. Our results suggest that a localized magnetic DW oscillator can be realized by appropriately adjusting the magnetic field and dc current. (C) 2015 The Japan Society of Applied Physics
Scientific journal, English - Reducing the switching current with a Gilbert damping constant in nanomagnets with perpendicular anisotropy
Keisuke Yamada; Kiyoaki Oomaru; Satoshi Nakamura; Tomonori Sato; Yoshinobu Nakatani
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 106, 4, 42402, Jan. 2015, Peer-reviwed, We report on current-induced magnetization switching in a nanomagnet with perpendicular anisotropy, and investigate the effects of the damping constant (alpha) on the switching current (I-sw) by varying the nanosecond-scale pulse current duration (t(p)), the saturation magnetization (M-s), and the magnetocrystalline anisotropy (K-u). The results show that reduction of alpha below a certain threshold (alpha(c)) is ineffective in reducing I-sw for short t(p). When t(p) is short, it is necessary to reduce both a and M-s simultaneously until ac is reached to reduce I-sw. The results presented here offer a promising route for the design of ultrafast information storage and logic devices using current-induced magnetization switching. (C) 2015 AIP Publishing LLC.
Scientific journal, English - 18pCM-10 Effect of the Gilbert damping constant on the switching current in the spin-transfer switching with the thermal fluctuation interaction
Yamada Keisuke; Nakatani Yoshinobu
Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS), 70, 963-963, 2015
Japanese - 18pCM-1 Domain wall manipulation by nanosecond pulse current
Taniguchi T.; Kim K.-J.; Tono T.; Moriyama T.; Nakatani Y.; Ono T.
Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS), 70, 954-954, 2015
Japanese - 23pAD-3 Simulation of the field-driven magnetic domain wall motion under the Dzyaloshinskii-Moriya interaction
Yamada Keisuke; Nakatani Yoshinobu
Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS), 70, 1198-1198, 2015
Japanese - 23pAD-1 Magnetic domain-wall oscillator controlled by magnetic field and dc current
Hiramatsu R.; Kim Kab-Jin; Taniguchi T.; Tono T.; Moriyama T.; Fukami S.; Yamanouchi M.; Ohno H.; Nakatani Y.; Ono T.
Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS), 70, 1196-1196, 2015
Japanese - 22pAH-12 Detection of Magnetic Vortex Core by the Ballistic Microstructure
Tanaka T.; Kawamura T.; Arakawa T.; Tanabe K.; Kobayashi K.; Yamada K.; Nakatani Y.; Ono T.
Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS), 70, 1193-1193, 2015
Japanese - Proposal for quantifying the Dzyaloshinsky-Moriya interaction by domain walls annihilation measurement
Ryo Hiramatsu; Kab-Jin Kim; Yoshinobu Nakatani; Takahiro Moriyama; Teruo Ono
JAPANESE JOURNAL OF APPLIED PHYSICS, IOP PUBLISHING LTD, 53, 10, 108001, Oct. 2014, Peer-reviwed, We show that the magnitude of the Dzyaloshinsky-Moriya interaction (DMI) can be determined by a field-driven domain-walls (DWs) annihilation measurement. It is predicted that the DMI induces antiparallel Neel DWs which form a metastable 360 degrees DW when they approach to each other. We find that an annihilation field, over which two DWs collide and vanish, is proportional to the magnitude of the DMI. This result suggests that the DMI can be quantified by a simple measurement of the annihilation field. (C) 2014 The Japan Society of Applied Physics
Scientific journal, English - Coupled oscillations of vortex cores confined in a ferromagnetic elliptical disk
Hiroshi Hata; Minori Goto; Akinobu Yamaguchi; Tomonori Sato; Yoshinobu Nakatani; Yukio Nozaki
PHYSICAL REVIEW B, AMER PHYSICAL SOC, 90, 10, 104418, Sep. 2014, Peer-reviwed, By solving the Thiele equation with simultaneous application of a radio-frequency (rf) magnetic field (h(rf)) and an rf spin current (j(sp)), the dynamic susceptibility of exchange-coupled vortices in response to hrf and jsp was obtained. It was found that the four eigenmodes expected for two vortices trapped in a magnetic elliptical disk were coupled to different components of h(rf) and j(sp). As a consequence, orthogonal h(rf) and j(sp) (which are simultaneously generated by the application of an rf current to an elliptical disk) can excite two modes with different eigenfrequencies. This result suggests that a fieldlike nonadiabatic torque caused by an rf spin current can be spectroscopically distinguished from the one caused by the rf magnetic field.
Scientific journal, English - Control of magnetic vortex core switching in a Pac-man disk using a single current pulse
Tomonori Sato; Keisuke Yamada; Yoshinobu Nakatani
APPLIED PHYSICS EXPRESS, IOP PUBLISHING LTD, 7, 7, 73003, Jul. 2014, Peer-reviwed, We report on the switching of the magnetic vortex core in a Pac-man disk using a nanosecond current pulse, investigated via micromagnetic simulations. The minimum core switching current density is reduced by 75% compared with that of a circular disk with the same diameter and thickness. The direction of the nucleation core is determined by the kinetic field of the out-of-plane component, which is induced by the core motion. We also show that the polarity of the core can be uniquely controlled by adjusting the direction of the current pulse. (C) 2014 The Japan Society of Applied Physics
Scientific journal, English - Switching of magnetic vortex core in elliptical disks by nanosecond field pulses
Keisuke Yamada; Tomonori Sato; Yoshinobu Nakatani; Shinya Kasai; Daichi Chiba; Kensuke Kobayashi; Andre Thiaville; Teruo Ono
APPLIED PHYSICS EXPRESS, IOP PUBLISHING LTD, 7, 6, 63008, Jun. 2014, Peer-reviwed, We report the switching of a magnetic vortex core in ferromagnetic elliptical disks induced by a nanosecond field pulse. We show that the switching probability depends on both the duration and amplitude of the field pulse. The minimum magnetic field required for the core switching depends also on the ellipticity of the disk. Micromagnetic simulations reproduce this behavior and reveal that there are two mechanisms of the core switching. (C) 2014 The Japan Society of Applied Physics
Scientific journal, English - Magnetization switching in a CoFeB/MgO magnetic tunnel junction by combining spin-transfer torque and electric field-effect
S. Kanai; Y. Nakatani; M. Yamanouchi; S. Ikeda; H. Sato; F. Matsukura; H. Ohno
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 104, 21, 212406, May 2014, Peer-reviwed, We propose and demonstrate a scheme for magnetization switching in magnetic tunnel junctions, in which two successive voltage pulses are applied to utilize both spin-transfer torque and electric field effect. Under this switching scheme, a CoFeB/MgO magnetic tunnel junction with perpendicular magnetic easy axis is shown to switch faster than by spin-transfer torque alone and more reliably than that by electric fields alone. (C) 2014 AIP Publishing LLC.
Scientific journal, English - Spin-transfer torque magnetoresistive random-access memory technologies for normally off computing (invited)
K. Ando; S. Fujita; J. Ito; S. Yuasa; Y. Suzuki; Y. Nakatani; T. Miyazaki; H. Yoda
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 115, 17, 172607, May 2014, Peer-reviwed, Most parts of present computer systems are made of volatile devices, and the power to supply them to avoid information loss causes huge energy losses. We can eliminate this meaningless energy loss by utilizing the non-volatile function of advanced spin-transfer torque magnetoresistive random-access memory (STT-MRAM) technology and create a new type of computer, i.e., normally off computers. Critical tasks to achieve normally off computers are implementations of STT-MRAM technologies in the main memory and low-level cache memories. STT-MRAM technology for applications to the main memory has been successfully developed by using perpendicular STT-MRAMs, and faster STT-MRAM technologies for applications to the cache memory are now being developed. The present status of STT-MRAMs and challenges that remain for normally off computers are discussed. (C) 2014 AIP Publishing LLC.
Scientific journal, English - Distribution of critical current density for magnetic domain wall motion
S. Fukami; M. Yamanouchi; Y. Nakatani; K. -J. Kim; T. Koyama; D. Chiba; S. Ikeda; N. Kasai; T. Ono; H. Ohno
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 115, 17, 17D508, May 2014, Peer-reviwed, The bit-to-bit distribution of a critical current density for magnetic domain wall (DW) motion is studied using Co/Ni wires with various wire widths (ws). The distribution inherently decreases with the w, and the ratio of standard deviation to average is 9.8% for wires with w = 40 nm. It is found that a self-distribution within one device, which is evaluated through repeated measurement, is a dominant factor in the bit-to-bit distribution. Micromagnetic simulation reveals that the distribution originates from DW configuration, which varies with device size. (C) 2014 AIP Publishing LLC.
Scientific journal, English - Effect of spin Hall torque on current-induced precessional domain wall motion
Yoko Yoshimura; Tomohiro Koyama; Daichi Chiba; Yoshinobu Nakatani; Shunsuke Fukami; Michihiko Yamanouchi; Hideo Ohno; Kab-Jin Kim; Takahiro Moriyama; Teruo Ono
APPLIED PHYSICS EXPRESS, IOP PUBLISHING LTD, 7, 3, 33005, Mar. 2014, Peer-reviwed, Two important mechanisms for current-induced domain wall (DW) dynamics, namely, precessional DW motion driven by the adiabatic spin transfer torque and steady DW motion induced by the spin Hall torque, have been proposed and experimentally confirmed. However, the effect of the spin Hall torque on precessional DW motion has not been reported yet. Here, we show that the spin Hall torque affects the precessional DW motion when the in-plane field is applied. It is found that the in-plane field induces a half rotation time difference during DW precession, which gives rise to the nonvanishing spin Hall torque on the precessional DW motion. (C) 2014 The Japan Society of Applied Physics
Scientific journal, English - Switching of magnetic vortex core in a Pac-man disk using a single field pulse
Tomonori Sato; Keisuke Yamada; Yoshinobu Nakatani
APPLIED PHYSICS EXPRESS, IOP PUBLISHING LTD, 7, 3, 33003, Mar. 2014, Peer-reviwed, We report on the switching of the magnetic vortex core in a Pac-man disk using a magnetic field pulse, investigated via micromagnetic simulations. The minimum core switching field is reduced by 72% compared with that of a circular disk with the same diameter and thickness. However, the core switches irregularly with respect to both the field pulse amplitude and duration. This irregularity is induced by magnetization oscillations that arise owing to the excitation of spin waves when the core annihilates. We show that the core switching can be controlled with the assist magnetic field and by changing the waveform. (C) 2014 The Japan Society of Applied Physics
Scientific journal, English - Electric Field-Induced Magnetization Switching in CoFeB-MgO-Static Magnetic Field Angle Dependence
Shun Kanai; Michihiko Yamanouchi; Shoji Ikeda; Yoshinobu Nakatani; Fumihiro Matsukura; Hideo Ohno
IEEE TRANSACTIONS ON MAGNETICS, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 50, 1, article number 4200103, Jan. 2014, Peer-reviwed, We investigate switching probabilities of electric field-induced magnetization switching in CoFeB/MgO based magnetic tunnel junction with perpendicular magnetic easy axis under static magnetic field with various directions. The switching takes place through magnetization precession with the period determined by the magnitude of the in-plane component of magnetic field. The experimental results are well reproduced by macro-spin simulation. The simulation reveals that decoherence induced by thermal fluctuations and/or other effects limit the switching probabilities in the present system.
Scientific journal, English - IEEE Transactions on Magnetics
S. Kanai; M. Yamanouchi; S. Ikeda; Y. Nakatani; F. Matsukura; H. Ohno
Electric field-induced magnetization switching in CoFeB-MgO-static magnetic field angle dependence, 50, 1, 4200103(1)-4200103(3), Jan. 2014, Peer-reviwed
Scientific journal, English - Micromagnetics of Domain Wall Dynamics in Soft Nanostrips
André Thiaville; Yoshinobu Nakatani
Nanomagnetism and Spintronics: Second Edition, Elsevier Inc., 261-313, Oct. 2013, Peer-reviwed, Spin-transfer torque manifests itself in two main geometries, either submicrometer diameter pillars composed of magnetic multilayers, flooded by a current perpendicular to plane (CPP), or nanowires with current flowing in their plane (CIP). The first situation can be described rather well, from the magnetic point of view, in the framework of the macrospin model (see Chapter 3 by Y. Suzuki). In the latter case, the typical situation is that of a magnetic domain wall under CIP current, with many internal degrees of freedom. In Chapter 5 by H. Kohno and G. Tatara, a simplest model of the domain wall, called collective coordinates model, has been introduced to study this question.In this chapter, we will address the entire manifold of the degrees of freedom in the domain wall by micromagnetic numerical simulations, and apply this to the physics of CIP spin transfer in magnetic domain walls. We will consider soft magnetic materials only, where domain wall structures and dynamics are controlled by magnetostatics. This corresponds to the largest part of experiments that have been performed up to now, soft magnetic materials having generally lower coercive forces and domain wall propagation fields. The experimental counterpart to this chapter can be found in Chapter 4, by T. Ono and T. Shinjo. After briefly introducing micromagnetics and the typology of domain walls in samples shaped into nanostrips, we start by reviewing the field-driven dynamics in such samples. This situation was indeed considered first, historically, and led to the introduction of several useful concepts. Prominent among them are the separation between steady-state and precessional regimes, and the existence of a maximum velocity for a domain wall. The spin-transfer torque-induced domain wall dynamics will then be addressed, considering first the implementation of the CIP spin transfer torque in micromagnetics, with several components as introduced by theory. Comparison will be made to the field-driven case, with similarities and differences highlighted.In the nascent field of nanomagnetism and spintronics, micromagnetics can be considered to play the role of a translator. There are on one side experiments and on the other side theories about interaction between magnetization and spin-polarized electrical currents. Micromagnetics is a tool that translates the equations of the latter into quantitative predictions that can be compared to the former. Considering the present state of the subject of this book, with rapidly advancing experiments and theories, keeping in touch those two aspects of research is very important for its sound development. This is the objective of this chapter. © 2014 Elsevier B.V. All rights reserved.
In book, English - Applied Physics Letters
S. Kanai; Y. Nakatani; M. Yamanouchi; S. Ikeda; F. Matsukura; H. Ohno
In-plane magnetic field dependence of electric field-induced magnetization switching, 103, 072408(1)-072408(4), 16 Aug. 2013, Peer-reviwed
Scientific journal, English - In-plane magnetic field dependence of electric field-induced magnetization switching
S. Kanai; Y. Nakatani; M. Yamanouchi; S. Ikeda; F. Matsukura; H. Ohno
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 103, 7, 72408, Aug. 2013, Peer-reviwed, Electric field-induced magnetization switching through magnetization precession is investigated as a function of in-plane component of external magnetic field for a CoFeB/MgO-based magnetic tunnel junction with perpendicular easy axis. The switching probability is an oscillatory function of the duration of voltage pulses and its magnitude and period depend on the magnitude of in-plane magnetic field. Experimental results are compared with simulated ones by using Landau-Lifshitz-Gilbert-Langevin equation, and possible factors determining the probability are discussed. (C) 2013 AIP Publishing LLC.
Scientific journal, English - Nature Communications
K. J. Kim; R. Hiramatsu; T. Koyama; K. Ueda; Y. Yoshimura; D. Chiba; K. Kobayashi; Y. Nakatani; S. Fukami; M. Yamanouchi; H. Ohno; H. Kohno; G. Tatara; T. Ono
Two-barrier stability that allows low-power operation in current-induced domain-wall motion, 4, 1-6, 17 Jun. 2013, Peer-reviwed
Scientific journal, English - Static and dynamic behavior of 360 degrees domain walls in patterned thin films
A. L. Gonzalez Oyarce; Y. Nakatani; C. H. W. Barnes
PHYSICAL REVIEW B, AMER PHYSICAL SOC, 87, 21, 214403, Jun. 2013, Peer-reviwed, We study the static and dynamic behavior of transverse domain walls and 360 degrees domain walls in a thin film of isotropic material including pinning effects caused by geometric defects in the form of triangular antinotches. In terms of the static interaction, our model reduces the domain walls to sources of magnetic charge, allowing an electrostatic-like description of their interaction. Such a concept was applied to both of these magnetic textures allowing us to estimate the shortest distance between the antinotches at which the domains walls can be located, while still being pinned. Regarding the domain walls' dynamical behavior, accurate micromagnetic simulations of our system were performed, characterizing their recombination times as well as showing that triangular notches allow the coherent movement of single and arrays of 360 degrees domain walls by pulses of spin current. This behavior could not be observed in single transverse walls given the long-range interaction that they present, impeding coherent domain wall motion. These findings allow us to estimate the maximum 360 degrees domain wall density, observing an increase by a factor of four when compared to systems based on single transverse domain walls, which potentially gives our system important industrial applications.
Scientific journal, English - Two-barrier stability that allows low-power operation in current-induced domain-wall motion
Kab-Jin Kim; Ryo Hiramatsu; Tomohiro Koyama; Kohei Ueda; Yoko Yoshimura; Daichi Chiba; Kensuke Kobayashi; Yoshinobu Nakatani; Shunsuke Fukami; Michihiko Yamanouchi; Hideo Ohno; Hiroshi Kohno; Gen Tatara; Teruo Ono
NATURE COMMUNICATIONS, NATURE PUBLISHING GROUP, 4, Article number 2011-2011, Jun. 2013, Peer-reviwed, True, Energy barriers in magnetization reversal dynamics have long been of interest because the barrier height determines the thermal stability of devices as well as the threshold force triggering their dynamics. Especially in memory and logic applications, there is a dilemma between the thermal stability of bit data and the operation power of devices, because larger energy barriers for higher thermal stability inevitably lead to larger magnetic fields (or currents) for operation. Here we show that this is not the case for current-induced magnetic domain-wall motion induced by adiabatic spin-transfer torque. By quantifying domain-wall depinning energy barriers by magnetic field and current, we find that there exist two different pinning barriers, extrinsic and intrinsic energy barriers, which govern the thermal stability and threshold current, respectively. This unique two-barrier system allows low-power operation with high thermal stability, which is impossible in conventional single-barrier systems.
Scientific journal, English - Current-Induced Magnetic Domain Wall Motion in a Co/Ni Nanowire with Structural Inversion Asymmetry
Tomohiro Koyama; Hiroshi Hata; Kab-Jin Kim; Takahiro Moriyama; Hironobu Tanigawa; Tetsuhiro Suzuki; Yoshinobu Nakatani; Daichi Chiba; Teruo Ono
APPLIED PHYSICS EXPRESS, IOP PUBLISHING LTD, 6, 3, 33001, Mar. 2013, Peer-reviwed, The authors have investigated the current-induced magnetic domain wall (DW) motion in perpendicularly magnetized Co/Ni nanowire with structural inversion asymmetry (SIA). In this system, DW motion to the direction of electric current flow, not electron flow, and high DW velocity up to 110 m/s were confirmed, which have never been observed in Co/Ni systems without SIA. In addition, we found that the DW velocity showed a strong dependence on the perpendicular magnetic field in the range of +/- 100 Oe. These results suggest that DW in the Co/Ni nanowire with SIA moves in the steady mode, not in the precessional mode. (C) 2013 The Japan Society of Applied Physics
Scientific journal, English - Real-time observation of electrical vortex core switching
Kunihiro Nakano; Kenji Tanabe; Ryo Hiramatsu; Daichi Chiba; Norikazu Ohshima; Shinya Kasai; Tomonori Sato; Yoshinobu Nakatani; Koji Sekiguchi; Kensuke Kobayashi; Teruo Ono
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 102, 7, 72405, Feb. 2013, Peer-reviwed, A single vortex-core switching induced by current injection into a ferromagnetic disk is detected in real time using a three-terminal device with the tunneling magnetoresistance junction. The real time observation reveals that the electrical core switching is completed within a few 100 ps. It is also found that the core switching takes place at the specific positions inside the disk. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4793212]
Scientific journal, English - Recording Density Limitation Explored by Head/Media Co-Optimization Using Genetic Algorithm and GPU-Accelerated LLG
Hiroshi Fukuda; Yoshinobu Nakatani
IEEE TRANSACTIONS ON MAGNETICS, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 48, 11, 3895-3898, Nov. 2012, Peer-reviwed, Designs of write-head geometry and multilayer recording-media composition (10-30 design variables) were optimized using a multi-objective genetic algorithm (GA) so as to maximize/minimize read/write (R/W) performance measures such as signal-to-noise ratio (SNR), magnetic write width (MWW), and thermal stability of media. A head-media co-design system using a general-purpose graphic processing unit (GPGPU)-accelerated Landau-Lifshitz-Gilbert (LLG) simulator and conventional finite element method (FEM) electromagnetic analysis enables thousands of R/W simulations required for GA to be performed within a practical amount of time. GA optimization of the write head showed recording density limitations and the impact of vertically scaling media/head-disk interface (HDI) dimensions on it. GA optimization of recording media showed a tradeoff relationship (trilemma) among MWW, SNR, and the thermal stability of media. The effectiveness of increasing complexity in media design such as the number of layers and the variable range of material properties on overcoming the trilemma were clarified. Design variables for optimization results scatter over relatively wide ranges, suggesting a wide variety of head-media designs. Finally, results of head-media co-designing suggested the importance of matching between write head and recording media.
Scientific journal, English - Current-induced magnetic domain wall motion below intrinsic threshold triggered by Walker breakdown
T. Koyama; K. Ueda; K. -J. Kim; Y. Yoshimura; D. Chiba; K. Yamada; J. -P. Jamet; A. Mougin; A. Thiaville; S. Mizukami; S. Fukami; N. Ishiwata; Y. Nakatani; H. Kohno; K. Kobayashi; T. Ono
NATURE NANOTECHNOLOGY, NATURE PUBLISHING GROUP, 7, 10, 635-639, Oct. 2012, Peer-reviwed, Controlling the position of a magnetic domain wall with electric current(1-11) may allow for new types of non-volatile memory and logic devices(10,12-14). To be practical, however, the threshold current density necessary for domain wall motion must be reduced below present values. Intrinsic pinning due to magnetic anisotropy(2), as recently observed in perpendicularly magnetized Co/Ni nanowires(15), has been shown to give rise to an intrinsic current threshold J(th)(0). Here, we show that domain wall motion can be induced at current densities 40% below J(th)(0) when an external magnetic field of the order of the domain wall pinning field is applied. We observe that the velocity of the domain wall motion is the vector sum of current- and field-induced velocities, and that the domain wall can be driven against the direction of a magnetic field as large as 2,000 Oe, even at currents below J(th)(0). We show that this counterintuitive phenomenon is triggered by Walker breakdown(16), and that the additive velocities provide a unique way of simultaneously determining the spin polarization of current and the Gilbert damping constant.
Scientific journal, English - Symmetry breaking in the formation of magnetic vortex states in a permalloy nanodisk
Mi-Young Im; Peter Fischer; Keisuke Yamada; Tomonori Sato; Shinya Kasai; Yoshinobu Nakatani; Teruo Ono
NATURE COMMUNICATIONS, NATURE PUBLISHING GROUP, 3, Article number 983-983, Jul. 2012, Peer-reviwed, True, The magnetic vortex in nanopatterned elements is currently attracting enormous interest. A priori, one would assume that the formation of magnetic vortex states should exhibit a perfect symmetry, because the magnetic vortex has four degenerate states. Here we show the first direct observation of an asymmetric phenomenon in the formation process of vortex states in a permalloy nanodisk using high-resolution full-field magnetic transmission soft X-ray microscopy. Micromagnetic simulations confirm that the intrinsic Dzyaloshinskii-Moriya interaction, which arises from the spin-orbit coupling due to the lack of inversion symmetry near the disk surface, as well as surface-related extrinsic factors, is decisive for the asymmetric formation of vortex states.
Scientific journal, English - Switching time of a single spin in linearly varying field
Yasutaro Uesaka; Yoshio Suzuki; Osamu Kitakami; Yoshinobu Nakatani; Nobuo Hayashi; Hiroshi Fukushima
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 111, 12, 123907, Jun. 2012, Peer-reviwed, We studied the switching time of a single spin in a field varying linearly in time using a micromagnetics simulation based on the Landau-Lifshitz-Gilbert equation. The applied field larger than the switching field or coercivity is not enough for a spin to switch but some duration of time is also necessary. We found that the value of C-1 defined by C-1 = integral(H - H-1)dt was constant when the rate of change in the field was larger than 10 x gamma H-k(2), where gamma is the gyromagnetic ratio with g value 2, H is the applied field, H-1 is a constant, and H-k is the anisotropy field of the spin. The integration is taken from the time the spin begins switching to the switching time. The equation is a generalized form of the equation, C-0 = (H - H-0)tau(sw), in a constant field H. Here, C-0 and H-0 are constants, and tau(sw) is the switching time. We found that C-1 in the region dH/dt > 10 x gamma H-K(2) and C-0 in the region H >> H-K are the same, but that H-1 does not coincide with H-0. We found that the head field rise time has a very small effect on the switching field and time of recording media. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4729897]
Scientific journal, English - Current-Induced Domain Wall Motion in Perpendicularly Magnetized Co/Ni Nanowire under In-Plane Magnetic Fields
Yoko Yoshimura; Tomohiro Koyama; Daichi Chiba; Yoshinobu Nakatani; Shunsuke Fukami; Michihiko Yamanouchi; Hideo Ohno; Teruo Ono
APPLIED PHYSICS EXPRESS, JAPAN SOC APPLIED PHYSICS, 5, 6, 63001, Jun. 2012, Peer-reviwed, We have investigated current-induced domain wall (DW) motion in a perpendicularly magnetized Co/Ni nanowire under in-plane (hard-axis) and perpendicular (easy-axis) external magnetic fields. The DW velocity was found to be almost independent of them in the range of +/- 50 Oe. The result shows that reliable device operation against an external magnetic field disturbance can be achieved using the present system. (C) 2012 The Japan Society of Applied Physics
Scientific journal, English - Temperature dependence of carrier spin polarization determined from current-induced domain wall motion in a Co/Ni nanowire
K. Ueda; T. Koyama; R. Hiramatsu; D. Chiba; S. Fukami; H. Tanigawa; T. Suzuki; N. Ohshima; N. Ishiwata; Y. Nakatani; K. Kobayashi; T. Ono
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 100, 20, 202407, May 2012, Peer-reviwed, We have investigated the temperature dependence of the current-induced magnetic domain wall (DW) motion in a perpendicularly magnetized Co/Ni nanowire at various temperatures and with various applied currents. The carrier spin polarization was estimated from the measured domain wall velocity. We found that it decreased more with increasing temperature from 100 K to 530 K than the saturation magnetization did. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4718599]
Scientific journal, English - Switching of a particle in inhomogeneous applied field
Y. Uesaka; H. Endo; Y. Suzuki; Y. Nakatani; N. Hayashi; H. Fukushima
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, ELSEVIER SCIENCE BV, 324, 7, 1272-1276, Apr. 2012, Peer-reviwed, We investigated switching field and its mechanism of a particle in inhomogeneous applied field using micromagnetics simulation and the following results were obtained. 1) The average switching field (ASF) is almost the same as the switching field in a uniform applied field when the gradient of the inhomogeneous field (FG) is small (< 0.6 kOe/nm) at any angle (xi) between the applied field and easy direction. The ASF decreases in small xi (< 60 degrees) and increases in large xi (> 60 degrees) with increasing the FG and/or with increasing zero applied field region when the FG is not small (> 0.6 kOe/nm). 2) The average switching field can also be determined from normalized particle size d/root A/K-u. Here, A is the exchange stiffness constant, K-u is the uniaxial anisotropy constant and d is the particle size. 3) Large FG is not necessarily important in a write head for BPM as long as the head field changes within one bit particle in the medium. (C) 2011 Elsevier B.V. All rights reserved.
Scientific journal, English - Domain wall dynamics driven by spin transfer torque and the spin-orbit field
Masamitsu Hayashi; Yoshinobu Nakatani; Shunsuke Fukami; Michihiko Yamanouchi; Seiji Mitani; Hideo Ohno
JOURNAL OF PHYSICS-CONDENSED MATTER, IOP PUBLISHING LTD, 24, 2, 24221-024221, Jan. 2012, Peer-reviwed, True, We have studied current-driven dynamics of domain walls when an in-plane magnetic field is present in perpendicularly magnetized nanowires using an analytical model and micromagnetic simulations. We model an experimentally studied system, ultrathin magnetic nanowires with perpendicular anisotropy, where an effective in-plane magnetic field is developed when current is passed along the nanowire due to the Rashba-like spin-orbit coupling. Using a one-dimensional model of a domain wall together with micromagnetic simulations, we show that the existence of such in-plane magnetic fields can either lower or raise the threshold current needed to cause domain wall motion. In the presence of the in-plane field, the threshold current differs for positive and negative currents for a given wall chirality, and the wall motion becomes sensitive to out-of-plane magnetic fields. We show that large non-adiabatic spin torque can counteract the effect of the in-plane field.
Scientific journal, English - Electric field-induced magnetization reversal in a perpendicular-anisotropy CoFeB-MgO magnetic tunnel junction
S. Kanai; M. Yamanouchi; S. Ikeda; Y. Nakatani; F. Matsukura; H. Ohno
APL, AIP Publishing, 101, 12, 122403, 2012, Peer-reviwed, The electric field-induced ∼180° magnetization reversal is realized for a sputtered CoFeB/MgO-based magnetic tunnel junction with perpendicular magnetic easy axis in a static external magnetic field. Application of bias voltage with nanoseconds duration results in a temporal change of magnetic easy axis in the free layer CoFeB to in-plane, which induces precessional motion of magnetization in the free layer. The magnetization reversal takes place when the bias voltage pulse duration is adjusted to a half period of the precession. We show that the back and forth magnetization reversal can be observed by using successive application of half-period voltage pulses.
Scientific journal - Stability of Vortex Structure on Core Switching
T. Sato; Y. Nakatani
J. Magn. Soc. Jpn., The Magnetics Society of Japan, 36, 3, 173-178-178, 2012, Peer-reviwed, The stability of the vortex structure on vortex core switching was investigated by using micromagnetic simulation. The method by the vortex core switching simulation by AC spin current is used to investigate this. Furthermore, the adequacy of the result was investigated by the evaluation of the magnetic energy. The switching simulation revealed that the vortex core did not switch around the transition dimension of magnetic disks between single-domain structure and the vortex structure in a remanent state, and the disk diameter needed to be increased to about 20 to 80 nm for stable vortex core switching compared with the stability limit in the remanent state. Furthermore, the results we obtained from our evaluation of magnetic energy agreed with the results obtained by simulating vortex core switching. Therefore, the result of the core switching simulation is also assured by the evaluation of magnetic energy.
Japanese - All-electrical operation of magnetic vortex core memory cell
K. Nakano; D. Chiba; N. Ohshima; S. Kasai; T. Sato; Y. Nakatani; K. Sekiguchi; K. Kobayashi; T. Ono
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 99, 26, 262505, Dec. 2011, Peer-reviwed, A single vortex-core switching in a ferromagnetic disk is detected in real time by using a three-terminal device with the tunneling magnetoresistance junction. We show that the device works as a vortex core memory cell, where reading and writing can be done in an all-electrical way: binary data corresponding to the core direction can be read out electrically as the amplitude of the output, while the data can be written electrically by applying a pulsed current. (C) 2011 American Institute of Physics. [doi:10.1063/1.3673303]
Scientific journal, English - Influence of Instabilities on High-Field Magnetic Domain Wall Velocity in (Co/Ni) Nanostrips
Keisuke Yamada; Jean-Pierre Jamet; Yoshinobu Nakatani; Alexandra Mougin; Andre Thiaville; Teruo Ono; Jacques Ferre
APPLIED PHYSICS EXPRESS, IOP PUBLISHING LTD, 4, 11, 113001, Nov. 2011, Peer-reviwed, The field-driven velocity of magnetic domain walls in nanostrips patterned in (Co/Ni) multilayer films with perpendicular anisotropy is studied by magnetooptical microscopy. By applying fields up to 250 mT, two peculiar features are revealed, which are beyond the simple one-dimensional model. First, above wall depinning, a velocity plateau is observed over a 150 mT field range. Then, at large fields, an important increase of velocity occurs. Micromagnetic simulations reproduce this behaviour and underline the nontrivial role of wall structure deformations in the appearance of this complexity. (C) 2011 The Japan Society of Applied Physics
Scientific journal, English - Spin-RAM for Normally-Off Computer
K. Ando; K. Yakushiji; H. Kubota; A. Fukushima; S. Yuasa; T. Kai; T. Kishi; N. Shimomura; H. Aikawa; M. Yoshikawa; T. Nagase; K. Nishiyama; E. Kitagawa; T. Daibou; M. Amano; S. Takahashi; M. Nakayama; S. Ikegawa; M. Nagamine; J. Ozeki; D. Watanabe; H. Yoda; T. Nozaki; Y. Suzuki; M. Oogane; S. Mizukami; Y. Ando; T. Miyazaki; Y. Nakatani
2011 11th Annual Non-Volatile Memory Technology Symposium Proceeding, IEEE, Nov. 2011, Peer-reviwed
International conference proceedings - Wire Width Dependence of Threshold Current Density for Domain Wall Motion in Co/Ni Nanowires
Tomohiro Koyama; Daichi Chiba; Kohei Ueda; Hironobu Tanigawa; Shunsuke Fukami; Tetsuhiro Suzuki; Norikazu Ohshima; Nobuyuki Ishiwata; Yoshinobu Nakatani; Teruo Ono
IEEE TRANSACTIONS ON MAGNETICS, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 47, 10, 3089-3091, Oct. 2011, Peer-reviwed, The authors have investigated wire width dependence of threshold current density for current-induced magnetic domain wall (DW) motion in perpendicularly magnetized Co/Ni nanowires. Threshold current density decreased with reducing the wire width, and the lowest threshold value of 1.6 x 10(11) A/m(2) was observed at the narrowest width of 36 nm. The micromagnetic simulation shows that the observed width dependence of threshold current density can be understood by the adiabatic spin transfer model.
Scientific journal, English - Effect of the Oersted field on a vortex core switching by pulse spin current
Yoshinobu Nakatani; Teruo Ono
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 99, 12, 122509, Sep. 2011, Peer-reviwed, We report the effect of the Oersted field on a vortex core switching in a circular magnetic disk by a pulse current obtained by simulation. The Oersted field of more than 500 Oe is appeared on the top and the bottom surfaces of the disk by the application of the pulse current of 1.57 x 10(12) A/m(2). The vortex core on each surface moves to the opposite direction each other by this field. The switching current decreases by half compared with the simulation without taking the Oersted field into account, and the switching current almost agrees with the experimental value. (C) 2011 American Institute of Physics. [doi:10.1063/1.3643140]
Scientific journal, English - Electric spectroscopy of vortex states and dynamics in magnetic disks
Minori Goto; Hiroshi Hata; Akinobu Yamaguchi; Yoshinobu Nakatani; Takehiro Yamaoka; Yukio Nozaki; Hideki Miyajima
PHYSICAL REVIEW B, AMER PHYSICAL SOC, 84, 6, 64406, Aug. 2011, Peer-reviwed, Spin-polarized radio frequency (RF) currents and RF-Oersted fields resonantly excite a magnetic vortex core confined in a micron-scale soft magnetic disk. In this study, we measured the rectifying voltage spectra caused by the anisotropic magnetoresistance oscillation due to the gyration of the vortex with different polarity and chirality. The measured spectra are presented such that we can determine the vortex properties and strength of the spin torques and Oersted field accurately and directly through analytical calculation.
Scientific journal, English - Electrical Investigation of Notch Width Dependence of Domain Wall Structure in Co/Ni Nanowires
Kouta Kondou; Ryo Hiramatsu; Tomohiro Koyama; Yoshinobu Nakatani; Daichi Chiba; Shunsuke Fukami; Nobuyuki Ishiwata; Teruo Ono
JAPANESE JOURNAL OF APPLIED PHYSICS, JAPAN SOC APPLIED PHYSICS, 50, 7, 73002, Jul. 2011, Peer-reviwed, We have investigated the notch width dependence of the domain wall structure by measuring the wall resistances in Co/Ni nanowires with perpendicular magnetization. Wall resistance was abruptly increased below a notch width of 43 nm. By comparing the experimental results with theoretical calculations of wall resistance and the micromagnetic simulation of wall energy, this increase in wall resistance was found to be caused by the change in the wall structure from the Bloch to Neel wall caused by the decreased notch width. (C) 2011 The Japan Society of Applied Physics
Scientific journal, English - Current-Induced Magnetic Domain Wall Motion in Co/Ni Nanowire at Low Temperature
Kohei Ueda; Tomohiro Koyama; Daichi Chiba; Kazutoshi Shimamura; Hironobu Tanigawa; Shunsuke Fukami; Tetsuhiro Suzuki; Norikazu Ohshima; Nobuyuki Ishiwata; Yoshinobu Nakatani; Teruo Ono
APPLIED PHYSICS EXPRESS, JAPAN SOC APPLIED PHYSICS, 4, 6, 63003, Jun. 2011, Peer-reviwed, Magnetic domain wall (DW) motion induced by currents in a perpendicularly magnetized Co/Ni nanowire has been investigated both at room temperature and low temperature. The threshold current density was almost independent of temperature, although the external magnetic field to depin a DW was doubled at low temperature. The result is consistent with the theory based on the adiabatic spin transfer model. (C) 2011 The Japan Society of Applied Physics
Scientific journal, English - Magnetic field insensitivity of magnetic domain wall velocity induced by electrical current in Co/Ni nanowire
T. Koyama; D. Chiba; K. Ueda; H. Tanigawa; S. Fukami; T. Suzuki; N. Ohshima; N. Ishiwata; Y. Nakatani; T. Ono
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 98, 19, 192509, May 2011, Peer-reviwed, We have investigated the velocity of magnetic domain wall (DW) motion induced by electric currents in a Co/Ni nanowire with a perpendicular magnetic anisotropy. The DW velocity increased as current density increased and the maximum velocity of 60 m/s was observed. Furthermore, the DW velocity was found to be almost independent of external perpendicular magnetic fields in the range of -50 to +50 Oe. The mechanism of the observed field insensitivity of the current induced DW motion is also discussed. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3590713]
Scientific journal, English - Electrical detection of vortex states in a ferromagnetic disk using the rectifying effect
M. Goto; H. Hata; Yamaguchi; Y. Nakatani; T. Yamaoka; Y. Nozaki
Journal of Applied Physics, The American Institute of Physics, 109, 7, 07D306 (3 pages), 18 Mar. 2011, Peer-reviwed
Scientific journal, English - Observation of the intrinsic pinning of a magnetic domain wall in a ferromagnetic nanowire
T. Koyama; D. Chiba; K. Ueda; K. Kondou; H. Tanigawa; S. Fukami; T. Suzuki; N. Ohshima; N. Ishiwata; Y. Nakatani; K. Kobayashi; T. Ono
NATURE MATERIALS, NATURE PUBLISHING GROUP, 10, 3, 194-197, Mar. 2011, Peer-reviwed, The spin transfer torque is essential for electrical magnetization switching(1,2). When a magnetic domain wall is driven by an electric current through an adiabatic spin torque, the theory predicts a threshold current even for a perfect wire without any extrinsic pinning(3). The experimental confirmation of this 'intrinsic pinning', however, has long been missing. Here, we give evidence that this intrinsic pinning determines the threshold, and thus that the adiabatic spin torque dominates the domain wall motion in a perpendicularly magnetized Co/Ni nanowire. The intrinsic nature manifests itself both in the field-independent threshold current and in the presence of its minimum on tuning the wire width. The demonstrated domain wall motion purely due to the adiabatic spin torque will serve to achieve robust operation and low energy consumption in spintronic devices(5-8).
Scientific journal, English - Current-induced domain wall motion in perpendicularly magnetized CoFeB nanowire
S. Fukami; T. Suzuki; Y. Nakatani; N. Ishiwata; M. Yamanouchi; S. Ikeda; N. Kasai; H. Ohno
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 98, 8, 82504, Feb. 2011, Peer-reviwed, Current-induced domain wall motion in perpendicularly magnetized CoFeB nanowires with a stack structure of Ta(1.0 nm)/CoFeB(1.2 nm)/MgO(2.0 nm)/Ta(1.0 nm) was investigated. Domain wall motion driven by adiabatic spin-transfer torque was observed at a current of about 74 mu A, corresponding to a current density of 6.2 x 10(7) A/cm(2). The obtained results were compared with those of a micromagnetic simulation and the spin polarization of the CoFeB was estimated to be 0.72. (C) 2011 American Institute of Physics. [doi:10.1063/1.3558917]
Scientific journal, English - Fast Micromagnetic Simulation of Vortex Core Motion by GPU
T. Sato; Y. Nakatani
J. Magn. Soc. Jpn,, The Magnetics Society of Japan, 35, 3, 163-170-170, 2011, Peer-reviwed, Micromagnetic simulation has been used to calculate magnetization distribution and dynamics in nanoscale magnetic materials. A method reducing the calculation time is needed because it requires prolonged periods for calculation. We propose a method of calculation to reduce the calculation time with a graphics processing unit (GPU). The speed with the proposed method is fifteen times faster than that with the conventional one with a CPU at maximum. Because a GPU has very fast single precision calculation units and relatively slow double precision calculation units, it is necessary to use single precision units for fast calculation with a GPU. The difference between the results of one calculation with single and double precision units is very small. However, this difference accumulates in simulations. There is a possibility the results may change due to this difference. This effect is investigated with static and dynamic simulations with a vortex structure in a nanodot. The relative differences in static and dynamic calculations are 10-6 and 0.04, respectively. These differences are sufficiently small for practical simulations. Therefore, a method with a GPU is useful to obtain micromagnetic simulations of vortex core motion.
English - Dependence of prefactor on the angle between an applied field and the easy axis for single-domain particles
Hiroshi Fukushima; Yasutaro Uesaka; Yoshinobu Nakatani; Nobuo Hayashi
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, ELSEVIER SCIENCE BV, 323, 2, 195-197, Jan. 2011, Peer-reviwed, The prefactor(attempt frequency) of particles with uniaxial anisotropy in an applied field at an oblique angle to the easy axis is studied systematically by calculating the smallest nonvanishing eigenvalue of the Fokker-Planck equation for several values of parameters under typical conditions in practical recording media. In the range of the damping constant 0.001-0.01, the prefactor increases with increasing the oblique angle from 0 degrees to 30 degrees, but for that angle of over 30 degrees the prefactor increases very little. It is shown that the dependence of the prefactor on the energy barrier height is almost the same in the range of the oblique angle 5-60 degrees of the applied field to the easy axis. It is confirmed that the prefactor under the conditions above takes from 10(8) to 10(10) per second. (C) 2010 Published by Elsevier B.V.
Scientific journal, English - Detection of vortex-core dynamics using current-induced self-bistable rectifying effect
M. Goto; H. Hata; A. Yamaguchi; H. Miyajima; Y. Nakatani; T. Yamaoka; Y. Nozaki
Journal of Physics, The Institute of Physics, 266, 1, 012080 (5 pages), Jan. 2011, Peer-reviwed
Scientific journal, English - Current-induced switching of magnetic vortex core in ferromagnetic elliptical disks
Keisuke Yamada; Shinya Kasai; Yoshinobu Nakatani; Kensuke Kobayashi; Teruo Ono
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 96, 19, 192508, May 2010, Peer-reviwed, We report the experimental observation and micromagnetics simulation of the current-induced switching of the magnetic vortex core in ferromagnetic elliptical disks. We found that the critical current density required for the core switching depends on the relative alignment between the current direction and the elliptical axes of the disk. The micromagnetics simulation results qualitatively reproduce the experimental findings, suggesting that the vortex core displacement induced by the current plays a significant role for the core switching rather than the core velocity. (C) 2010 American Institute of Physics. [doi:10.1063/1.3428792]
Scientific journal, English - Simulation of magnetization switching by electric-field manipulation of magnetic anisotropy
D. Chiba; Y. Nakatani; F. Matsukura; H. Ohno
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 96, 19, 192506, May 2010, Peer-reviwed, Electrical anisotropy modulation was recently observed in ferromagnetic semiconductors and metals. The authors have investigated magnetization switching through magnetic anisotropy modulation induced by external electric field by means of simulation. Macrospin simulation using Landau-Lifshitz-Gilbert equation shows that switching is possible by controlling magnetic anisotropy for appropriate sets of parameters. The condition for quasistatic magnetization switching is also presented, in which magnetization direction is determined to minimize the magnetic free energy. (C) 2010 American Institute of Physics. [doi:10.1063/1.3428959]
Scientific journal, English - High efficient spin transfer torque writing on perpendicular magnetic tunnel junctions for high density MRAMs
Tatsuya Kishi; Toshihiko Nagase; Masatoshi Yoshikawa; Katsuya Nishiyama; Eiji Kitagawa; Tadaomi Daibou; Minoru Amano; Naoharu Shimomura; Shigeki Takahashi; Tadashi Kai; Masahiko Nakayama; Hisanori Aikawa; Sumio Ikegawa; Makoto Nagamine; Junichi Ozeki; Shigemi Mizukami; Mikihiko Oogane; Yasuo Ando; Shinji Yuasa; Kei Yakushiji; Hitoshi Kubota; Yoshishige Suzuki; Yoshinobu Nakatani; Terunobu Miyazaki; Koji Ando
Curr. Appl. Phys., ELSEVIER, 10, 1, e87-89, Apr. 2010, Peer-reviwed, An Fe-based perpendicular alloy with small damping constant was applied to an MTJ storage layer and small switching current of 9 mu A was obtained for a write current width of 5 ms. The efficiency of spin transfer torque writing was proved to be higher than those for in-plane MTJs. The estimated Ic for the MTJ with 50 nsec pulse width is lower than 20 mu A and smaller than the drive currents of CMOS transistor at Gbits density. (C) 2010 Elsevier B.V. All rights reserved.
Scientific journal, English - Control of Multiple Magnetic Domain Walls by Current in a Co/Ni Nano-Wire
Daichi Chiba; Gen Yamada; Tomohiro Koyama; Kohei Ueda; Hironobu Tanigawa; Shunsuke Fukami; Tetsuhiro Suzuki; Norikazu Ohshima; Nobuyuki Ishiwata; Yoshinobu Nakatani; Teruo Ono
APPLIED PHYSICS EXPRESS, JAPAN SOC APPLIED PHYSICS, 3, 7, 73004, 2010, Peer-reviwed, All-electrical control and local detection of multiple magnetic domain walls in perpendicularly magnetized Co/Ni nano-wires were demonstrated. A series of domain walls was reproducibly shifted in the same direction by the current, keeping the distance between the walls almost the same. Furthermore, the walls can be shifted back and forth depending on the direction of the pulsed currents. (C) 2010 The Japan Society of Applied Physics
Scientific journal, English - Relation between critical current of domain wall motion and wire dimension in perpendicularly magnetized Co/Ni nanowires
S. Fukami; Y. Nakatani; T. Suzuki; K. Nagahara; N. Ohshima; N. Ishiwata
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 95, 23, 232504, Dec. 2009, Peer-reviwed, We investigated the relation between critical current of domain wall motion and wire dimension by using perpendicularly magnetized Co/Ni nanowires with different widths and thicknesses. The critical current, I(c), became less than 0.2 mA when w < 100 nm, suggesting that magnetic random access memory with domain wall motion can replace conventional embedded memories. In addition, in agreement with theory, the critical current density, j(c), decreased as wire width decreased and became much less than 5 x 10(7) A/cm(2) when w < 100 nm. We also performed a micromagnetic simulation and obtained good agreement between the experiment and simulation, although a few discrepancies were found. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3271827]
Scientific journal, English - Domain Wall Motion Induced by Electric Current in a Perpendicularly Magnetized Co/Ni Nano-Wire
Hironobu Tanigawa; Tomohiro Koyama; Gen Yamada; Daichi Chiba; Shinya Kasai; Shunsuke Fukami; Tetsuhiro Suzuki; Norikazu Ohshima; Nobuyuki Ishiwata; Yoshinobu Nakatani; Teruo Ono
APPLIED PHYSICS EXPRESS, IOP PUBLISHING LTD, 2, 5, 53002, May 2009, Peer-reviwed, The authors show experimental results on domain wall motion induced by electric current in a Co/Ni nano-wire with perpendicular magnetic anisotropy. The motion was detected electrically by using the anomalous Hall effect. Threshold current density for the domain wall motion was found to decrease with decreasing the wire width, where the minimum threshold current density of approximately 5 x 10(11) A/m(2) was observed for the wire width of 70 nm. (c) 2009 The Japan Society of Applied Physics
Scientific journal, English - Switching field and mechanism of cubic and flat square particles
Y. Uesaka; H. Endo; Y. Nakatani; N. Hayashi; H. Fukushima
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 105, 7, 07C126, Apr. 2009, Peer-reviwed, Switching fields and mechanisms of cubic and flat square particles were investigated using computer simulation. The switching fields can be estimated from the nucleation fields obtained from the analytical equation for the coherent rotation or the curling modes of a sphere with the same diameter as the cubic particle or of an oblate spheroid with the same length of the principal axes as the flat square particle. When the magnetic moments rotate coherently in the initial stage (M(zav)/M(s) similar to 0.9, M(zav) is the average magnetization in the easy direction and M(s) is the saturation magnetization), the nucleation field of the coherent rotation mode accounts for the switching field. The switching fields of the flat square particle with chips were also investigated when the exchange stiffness constant was not small (= 1.0 x 10(-6) erg/cm). It was found that the chips increase the switching field and that the sum of the anisotropy field and the field due to shape anisotropy calculated from the average demagnetizing fields in the three directions (x, y, z) accounts for the switching field. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3076150]
Scientific journal, English - Magnetic field dependence of rectification radio frequency current flowing through a single layered ferromagnetic wire
A. Yamaguchi; K. Motoi; H. Miyajima; Y. Nakatani
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 105, 7, 07D301, Apr. 2009, Peer-reviwed, The spin and electric charge of electrons in nanoscale artificial magnetic systems exhibit peculiar behaviors especially in a radio-frequency (rf) region via spin-wave excitations. One of the interesting effects is the rectification of the rf current in nanomagnets. We present a detailed experimental magnetic field dependence of the rectifying spectrum induced by a rf current flowing through the ferromagnetic wire and discuss in terms of the quantized spin-wave modes excited by the microwave injection. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3056143]
Scientific journal, English - Micromagnetics of Domain-Wall Dynamics in Soft Nanostrips
André Thiaville; Yoshinobu Nakatani
Nanomagnetism and Spintronics, Elsevier, 231-276, 2009, Peer-reviwed, This chapter addresses the degrees of freedom in the domain wall by micromagnetic numerical simulations, and applies this to the physics of CIP spin transfer in magnetic domain walls. It considers soft magnetic materials only, where domain-wall structures and dynamics are controlled by magnetostatics. This corresponds to soft magnetic materials having generally lower coercive forces and domain-wall propagation fields. After briefly introducing micromagnetics and the typology of domain walls in samples shaped into nanostrips, the chapter reviews the field-driven dynamics in such samples. Consideration of this situation, historically, has led to the introduction of several useful concepts. Prominent among these concepts are the separation between linear and non-linear regimes, and the existence of a maximum velocity for a domain wall. Spin transfer torque (STT)-induced domain-wall dynamics are addressed, considering first the implementation of the CIP STT in micromagnetics, with several components as introduced by theory. Micromagnetics is a tool that translates the equations of spin-polarized electrical currents into quantitative predictions that can be compared to magnetization. © 2009 Copyright © 2009 Elsevier B.V. All rights reserved.
In book, English - Probing the Spin Polarization of Current by Soft X-Ray Imaging of Current-Induced Magnetic Vortex Dynamics
Shinya Kasai; Peter Fischer; Mi-Young Im; Keisuke Yamada; Yoshinobu Nakatani; Kensuke Kobayashi; Hiroshi Kohno; Teruo Ono
PHYSICAL REVIEW LETTERS, AMER PHYSICAL SOC, 101, 23, 237203-237203, Dec. 2008, Peer-reviwed, True, Time-resolved soft x-ray transmission microscopy is applied to image the current-induced resonant dynamics of the magnetic vortex core realized in a micron sized Permalloy disk. The high spatial resolution better than 25 nm enables us to observe the resonant motion of the vortex core. The result also provides the spin polarization of the current to be 0.67 +/- 0.16 for Permalloy by fitting the experimental results with an analytical model in the framework of the spin-transfer torque.
Scientific journal, English - Dynamical Pinning of a Domain Wall in a Magnetic Nanowire Induced by Walker Breakdown
Hironobu Tanigawa; Tomohiro Koyama; Maciej Bartkowiak; Shinya Kasai; Kensuke Kobayashi; Teruo Ono; Yoshinobu Nakatani
PHYSICAL REVIEW LETTERS, AMER PHYSICAL SOC, 101, 20, 207203-207203, Nov. 2008, Peer-reviwed, True, Transmission probability of a domain wall through a magnetic nanowire is investigated as a function of the external magnetic field. A very intriguing phenomenon is found that the transmission probability shows a significant drop after exceeding the threshold driving field, which contradicts our intuition that a domain wall is more mobile in the higher magnetic field. The micromagnetics simulation reveals that the domain wall motion in the wire with finite roughness causes the dynamical pinning due to the Walker breakdown, which semiquantitatively explains our experimental results.
Scientific journal, English - Electrical rectification effect in single domain magnetic microstrips: A micromagnetics-based analysis
Andre Thiaville; Yoshinobu Nakatani
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 104, 9, 93701, Nov. 2008, Peer-reviwed, Upon passing an ac electrical current along magnetic micro- or nanostrips, the measurement of a dc voltage that depends sensitively on current frequency and applied field has been recently reported by Yamaguchi et al. [Appl. Phys. Lett. 90, 182507 (2007); e-print arXiv: 0710.2172; Phys. Rev. B 78, 104401 (2008)]. It was attributed to the excitation of spin waves by the spin transfer torque, leading to a time-varying anisotropic magnetoresistance, and by mixing of ac current and resistance to a dc. voltage. We have performed a quantitative analysis by micromagnetics including the spin transfer torque terms considered usually of this situation. The signals found from the spin transfer torque effect are several orders of magnitude below the experimental values, even if a static inhomogeneity of magnetization (the so-called ripple) is taken into account. On the other hand, the presence of a small nonzero average Oersted field is shown to be consistent with the full set of experimental results, both qualitatively and quantitatively. We examine, quantitatively, several sources for this average field and point to the contacts of the sample as a likely origin. (c) 2008 American Institute of Physics. [DOI: 10.1063/1.3006005]
Scientific journal, English - Switching magnetic vortex core by a single nanosecond current pulse
Keisuke Yamada; Shinya Kasai; Yoshinobu Nakatani; Kensuke Kobayashi; Teruo Ono
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 93, 15, 152502, Oct. 2008, Peer-reviwed, In a ferromagnetic nanodisk, the magnetization tends to swirl around in the plane of the disk and can point either up or down at the center of this "magnetic vortex." This binary state can be useful for information storage. It is demonstrated that a single nanosecond current pulse can switch the core polarity. This method also provides the precise control of the core direction, which constitutes fundamental technology for realizing a vortex core memory. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3001588]
Scientific journal, English - Control of Domain Wall Position by Electrical Current in Structured Co/Ni Wire with Perpendicular Magnetic Anisotropy
Tomohiro Koyama; Gen Yamada; Hironobu Tanigawa; Shinya Kasai; Norikazu Ohshima; Shunsuke Fukami; Nobuyuki Ishiwata; Yoshinobu Nakatani; Teruo Ono
APPLIED PHYSICS EXPRESS, IOP PUBLISHING LTD, 1, 10, 101303, Oct. 2008, Peer-reviwed, We report the direct observation of the current-driven domain wall (DW) motion by magnetic force microscopy in a structured Co/Ni wire with perpendicular magnetic anisotropy. The wire has notches to define the DW position. It is demonstrated that single current pulses can precisely control the DW position from notch to notch with high DW velocity of 40 m/s. (c) 2008 The Japan Society of Applied Physics
Scientific journal, English - Magnetization vector manipulation by electric fields
D. Chiba; M. Sawicki; Y. Nishitani; Y. Nakatani; F. Matsukura; H. Ohno
NATURE, NATURE PUBLISHING GROUP, 455, 7212, 515-518, Sep. 2008, Peer-reviwed, Conventional semiconductor devices use electric fields to control conductivity, a scalar quantity, for information processing. In magnetic materials, the direction of magnetization, a vector quantity, is of fundamental importance. In magnetic data storage, magnetization is manipulated with a current-generated magnetic field (Oersted-Ampere field), and spin current(1,2) is being studied for use in non- volatile magnetic memories(3,4). To make control of magnetization fully compatible with semiconductor devices, it is highly desirable to control magnetization using electric fields. Conventionally, this is achieved by means of magnetostriction produced by mechanically generated strain through the use of piezoelectricity(5-8). Multiferroics(9,10) have been widely studied in an alternative approach where ferroelectricity is combined with ferromagnetism. Magnetic- field control of electric polarization has been reported in these multiferroics using the magnetoelectric effect, but the inverse effect - direct electrical control of magnetization - has not so far been observed(11). Here we show that the manipulation of magnetization can be achieved solely by electric fields in a ferromagnetic semiconductor, (Ga,Mn)As. The magnetic anisotropy, which determines the magnetization direction, depends on the charge carrier (hole) concentration in (Ga,Mn) As. By applying an electric field using a metal - insulator - semiconductor structure(12-14), the hole concentration and, thereby, the magnetic anisotropy can be controlled, allowing manipulation of the magnetization direction.
Scientific journal, English - Long-range vortex domain wall displacement induced by an alternating current: Micromagnetic simulations
Peter Warnicke; Yoshinobu Nakatani; Shinya Kasai; Teruo Ono
PHYSICAL REVIEW B, AMER PHYSICAL SOC, 78, 1, 12413, Jul. 2008, Peer-reviwed, A magnetic vortex domain wall, confined in a Permalloy nanowire with periodically varying width, is brought to resonance and long-range motion by means of a spin-polarized alternating current in micromagnetical simulations. The long-range direction of motion is found to be dependent on the vortex chirality but independent of the vortex polarity. Compared to the case where a direct current is used to move the vortex domain wall, the threshold current density for long-range motion is significantly reduced.
Scientific journal, English - Single-shot measurements of spin-transfer switching in CoFeB/MgO/CoFeB magnetic tunnel junctions
Hiroyuki Tomita; Katuaki Konishi; Takayuki Nozaki; Hitoshi Kubota; Akio Fukushima; Kay Yakushiji; Shinji Yuasa; Yoshinobu Nakatani; Teruya Shinjo; Masashi Shiraishi; Yoshishige Suzuki
APPLIED PHYSICS EXPRESS, IOP PUBLISHING LTD, 1, 6, 61303, Jun. 2008, Peer-reviwed, Real-time measurements of spin-transfer induced magnetization switching were performed at room temperature on elliptical CoFeB/MgO/CoFeB magnetic tunnel junctions (60 x 170 nm(2)) using a storage oscilloscope. Free layer thickness and thermal stability factor (KuV/k(B)T) were 2 nm and 17, respectively. Under small dc current with short rise time (200 ps), the switching processes essentially comprised long waiting time and short transition time (less than 400 ps). We found, for the first time, that switching probability density was considerably lower for few ns after the rise of the current, and became constant later. Existence of this "non-reactive time" could be a critical issue for fast writing applications. (C) 2008 The Japan Society of Applied Physics.
Scientific journal, English - Single shot detection of the magnetic domain wall motion by using tunnel magnetoresistance effect
Kouta Kondou; Norikazu Ohshima; Shinya Kasai; Yoshinobu Nakatani; Teruo Ono
APPLIED PHYSICS EXPRESS, JAPAN SOC APPLIED PHYSICS, 1, 6, 61302, Jun. 2008, Peer-reviwed, Magnetic domain wall (DW) dynamics in submicron ferromagnetic wires has been investigated in real-time regime by using tunneling magneto resistance effect. The DW velocity as a function of magnetic field increases at low field range and takes a local maximum. After stagnation, the velocity starts to increase again. This is a typical signature of the Walker breakdown. Above the Walker field, the real-time traces of individual events show complex behaviors, which suggest the stochastic nature of the DW motion. (C) 2008 The Japan Society of Applied Physics.
Scientific journal, English - Magnetic domain wall oscillator
Teruo Ono; Yoshinobu Nakatani
APPLIED PHYSICS EXPRESS, JAPAN SOC APPLIED PHYSICS, 1, 6, 61301, Jun. 2008, Peer-reviwed, We show that the rotation of a magnetic domain wall (DW) can be induced by the injection of a dc current into a magnetic wire with a DW. A novel three-terminal device that produces microwaves by utilizing the current-induced DW rotation is proposed. The frequency of the microwaves can be tuned by adjusting the current density through the wire, and the amplitude of the microwaves can be regulated through a dc bias applied to the magnetic tunnel junction. (C) 2008 The Japan Society of Applied Physics.
Scientific journal, English - Development of High-speed Differential-Susceptibility Measuring Equipment
KAJI T.; ENDO H.; UESAKA Y.; NAKATANI Y.
Transactions of the Magnetics Society of Japan, The Magnetics Society of Japan (MSJ), 32, 3, 244-249, 01 Apr. 2008, We developed high-speed differential-susceptibility measuring equipment to examine thermal fluctuations in magnetic materials. In this study, we measured the dependence of the differential-susceptibility of a magnetic tape on a magnetic field by using the equipment. When the sweep speed of the magnetic field changed from high to low in the order of ms, the magnetic field that gave the maximum differential susceptibility shifted from a high to a low magnetic field due to thermal fluctuations. However, when the sweep speed of the magnetic field changed from high to low in the order of μs, the shift in magnetic field was not clearly detected. The time when the magnetization in the easy direction changed from the residual to the zero state obtained from a linear field, and the time obtained from the constant field, which is the same as the coercivity of the linear field, were calculated using micromagnetic simulations. From the ratio of the two times and from an experimental time when the applied field reached coercivity, a time that could be applied to Sharrock's equation was obtained. In order to fit the experimental results to Sharrock's equation, Ku must be much smaller than the experimental value and H0 must be much smaller than Hk (H0/Hk=0.38). Here, Ku, Hk, and H0 are anisotropy constat, anisotropy field, and coercivity at 0K.
Japanese - Nucleation and dynamics of magnetic vortices under spin-polarized current
Yoshinobu Nakatani; Junya Shibata; Gen Tatara; Hiroshi Kohno; Andre Thiaville; Jacques Miltat
PHYSICAL REVIEW B, AMER PHYSICAL SOC, 77, 1, 14439, Jan. 2008, Peer-reviwed, Spin-polarized current in a ferromagnet is known to lead to the instability of the uniformly magnetized state. In this paper, it is demonstrated by micromagnetic simulations that, in films or wide wires, the above instability is followed by the formation of magnetic vortices. Subsequent magnetization dynamics is also studied in terms of vortices, which includes pair dynamics and pair annihilation. Using a simple analytical model that considers the vortices as points, the dynamics of two interacting vortices under the current is classified according to their vorticity and polarity. This explains well the essential features of the simulation results.
Scientific journal, English - Transient domain wall displacement under spin-polarized current pulses
A. Thiaville; Y. Nakatani; F. Piechon; J. Miltat; T. Ono
EUROPEAN PHYSICAL JOURNAL B, SPRINGER, 60, 1, 15-27, Nov. 2007, Peer-reviwed, This paper investigates the non steady-state displacement of magnetic domain walls in a nanostrip submitted to a time-dependent spin-polarized current flowing along the nanostrip. First, numerical micromagnetic simulations show that a domain wall can move under application of a current pulse, and that the displacement resulting from a conversion of the domain wall structure is quantized. The numerical findings are subsequently explained in the framework of simplified analytic models, namely the 1D model and the point-core vortex model. We then introduce the concept of an angle linked to the magnetization of a general domain wall, and show that it allows understanding the transient phenomena quite generally. Simple analytic formulas are derived and compared to experiments. For this, charts are given for the key parameters of the domain wall mechanics, as obtained from numerical micromagnetic simulations. We finally discuss the limitations of this work, by looking at the influence of temperature elevation under current, presence of a non-adiabatic term, and of disorder.
Scientific journal, English - Rectification of radio frequency current in ferromagnetic nanowire
A. Yamaguchi; H. Miyajima; T. Ono; Y. Suzuki; S. Yuasa; A. Tulapurkar; Y. Nakatani
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 90, 18, 182507, Apr. 2007, Peer-reviwed, The authors report the rectification of a constant wave radio frequency (rf) current by using a single-layer magnetic nanowire; a direct-current voltage is resonantly generated when the rf current flows through the nanowire. The mechanism of the rectification is discussed in terms of the spin-torque diode effect reported for magnetic tunnel junction devices, and the rectification is shown to be directly attributable to resonant spin wave excitation by the rf current. (C) 2007 American Institute of Physics.
Scientific journal, English - Electrical switching of the vortex core in a magnetic disk
Keisuke Yamada; Shinya Kasai; Yoshinobu Nakatani; Kensuke Kobayashi; Hiroshi Kohno; Andre Thiaville; Teruo Ono
NATURE MATERIALS, NATURE PUBLISHING GROUP, 6, 4, 269-273, Apr. 2007, Peer-reviwed, True, A magnetic vortex is a curling magnetic structure realized in a ferromagnetic disk, which is a promising candidate for a memory cell for future non-volatile data-storage devices(1). Thus, an understanding of the stability and dynamical behaviour of the magnetic vortex is a major requirement for developing magnetic data-storage technology. Since the publication of experimental proof for the existence of a nanometre-scale core with out-of-plane magnetization in a magnetic vortex(2), the dynamics of vortices have been investigated intensively(3-10). However, a way to electrically control the core magnetization, which is a key for constructing a vortex-core memory, has been lacking. Here, we demonstrate the electrical switching of the core magnetization by using the current-driven resonant dynamics of the vortex; the core switching is triggered by a strong dynamic field that is produced locally by a rotational core motion at a high speed of several hundred metres per second. Efficient switching of the vortex core without magnetic-field application is achieved owing to resonance. This opens up the potentiality of a simple magnetic disk as a building block for spintronic devices such as a memory cell where the bit data is stored as the direction of the nanometre-scale core magnetization.
Scientific journal, English - Magnetic vortex dynamics induced by spin-transfer torque
J. Shibata; Y. Nakatani; G. Tatara; H. Kohno; Y. Otani
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, ELSEVIER SCIENCE BV, 310, 2, 2041-2042, Mar. 2007, Peer-reviwed, We theoretically study the dynamics of a magnetic vortex under spin-polarized electric current in ferromagnets. The equation of motion of the vortex in terms of collective coordinates is derived. We compare our theory with recent experiments for current-induced vortex displacement and resonance motion in a ferromagnetic nanodot. Our estimate for the displacement and the resonance frequency shows a good agreement with the experiment. We also study the current-induced motion of a vortex wall in a ferromagnetic thin wire. (c) 2006 Elsevier B.V. All rights reserved.
Scientific journal, English - Magnetization reversal in a ferromagnetic circular dot under current induced resonant excitation
Kasai S; Nakatani Y; Kobayashi K; Kohno H; Ono T
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 310, 2, 2351-2352, Mar. 2007, Peer-reviwed - Switching times of a single-domain particle in a field inclined off the easy axis
Hiroshi Fukushima; Yasutaro Uesaka; Yoshinobu Nakatani; Nobuo Hayashi
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 101, 1, 13901, Jan. 2007, Peer-reviwed, By solving Brown's Fokker-Planck equation numerically with the spherical harmonics, the magnetization reversal of a single-domain particle in a field at an oblique angle up to 45 degrees to the easy axis is investigated. Different from the usual definition, the switching time is defined as the time when the averaged z component of the magnetization reaches 90% of its final value. The switching times of the particle under various conditions are calculated. When the oblique angle of the field is 30 degrees-45 degrees and its magnitude is larger than the Stoner-Wohlfarth limit (H-sw), the switching time is dependent slightly on the oblique angle and magnitude of the field, and the temperature. For the oblique angle of 5 degrees, the switching time depends largely on the magnitude of the field and the temperature. When the magnitude of the field is less than H-sw, the switching time is dependent largely on the oblique angle and the temperature. Effects of the damping constant are also studied. (c) 2007 American Institute of Physics.
Scientific journal, English - Formation of magnetic clusters in perpendicular thin films
H. Endo; Y. Uesaka; Y. Nakatani; N. Hayashi; H. Fukushima
IEEE TRANSACTIONS ON MAGNETICS, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 42, 10, 2969-2971, Oct. 2006, Peer-reviwed, The formation and growing process of magnetic clusters in perpendicular thin films were investigated using micromagnetic simulation. Two estimation methods of cluster size were proposed. CS(area) was defined as the diameter of the circle which has the same area as the reversed region. CS(corr) was defined from the correlation between magnetizations of adjacent grains. These cluster sizes were calculated in the demagnetizing process. The shape of the cluster can be estimated from comparison between CS(area) and CS(corr). If CS(area) is larger than CS(corr), string shape clusters are formed. If CS(area) coincides with CS(corr), there are nonstring shape clusters. In order to make cluster size,;mall in the demagnetizing process it is useful for the perpendicular thin film to have grain size dispersion.
Scientific journal, English - Current-driven resonant excitation of magnetic vortices
Shinya Kasai; Yoshinobu Nakatani; Kensuke Kobayashi; Hiroshi Kohno; Teruo Ono
PHYSICAL REVIEW LETTERS, AMERICAN PHYSICAL SOC, 97, 10, 107204-107204, Sep. 2006, Peer-reviwed, True, A magnetic vortex core in a ferromagnetic circular nanodot has a resonance frequency originating from the confinement of the vortex core. By the micromagnetic simulation including the spin-transfer torque, we show that the vortex core can be resonantly excited by an ac (spin-polarized) current through the dot and that the resonance frequency can be tuned by the dot shape. The resistance measurement under the ac current successfully detects the resonance at the frequency consistent with the simulation.
Scientific journal, English - Switching time of single magnetic particle and maximum recording frequency of perpendicular magnetic recording
Y Uesaka; H Endo; Y Nakatani; N Hayashi; H Fukushima
IEEE TRANSACTIONS ON MAGNETICS, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 42, 7, 1892-1895, Jul. 2006, Peer-reviwed, We investigated the switching time of a magnetic particle-which may impose limits on magnetic recording frequency-by computer simulation. We found that the difference in switching time between low and high temperatures decreases with increasing the angle between the applied field and the easy direction, and scarcely changes with temperature if the angle is larger than a few degrees. This can be explained by considering the energy contour and locus of magnetization in switching. The switching times derived by using divided models, in which the particle is divided into 2 x 2 x 2 or 4 x 4 x 4 cells, are smaller than those derived by using an undivided model. But the difference between the switching times derived with the divided and undivided models is less than 1% if the angle is larger than 1 degrees. We derived equations to express the switching times of the particle for the divided models at 0, and we used the equations to estimate the maximum recording frequency in perpendicular recording.
Scientific journal, English - Threshold current of domain wall motion under extrinsic pinning, beta-term and non-adiabaticity
Gen Tatara; Toshihiko Takayama; Hiroshi Kohno; Junya Shibata; Yoshinobu Nakatani; Hidetoshi Fukuyama
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 75, 6, 64708, Jun. 2006, Peer-reviwed, Threshold current of domain wall motion under spin-polarized electric current in ferromagnets is theoretically studied based on the equation of motion of a wall in terms of collective coordinates. Effects of non-adiabaticity and a so-called beta-term in Landau-Lifshitz equation, which are described by the same term in the equation of motion of a wall, are taken into account as well as extrinsic pinning. It is demonstrated that there are four different regimes characterized by different dependence of threshold on extrinsic pinning, hard-axis magnetic anisotropy, non-adiabaticity and beta.
Scientific journal, English - Influence of in-plane field on the thermal stability of perpendicular media
Y Uesaka; H Endo; N Kodama; Y Nakatani; N Hayashi; H Fukushima
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 99, 8, Apr. 2006, Peer-reviwed, In order to investigate the effect of single pole type head scanning on output signal stability of perpendicular media, 2 kOe static magnetic field was applied to the media. The results are as follows. Coupling of the in-plane component of the magnetic field and thermal agitation decrease output signal. On the other hand, the perpendicular component of the magnetic field scarcely affects the stability of the output signal. Exchange interaction between grains in the recording layer increases the stability of the output signal. Easy axis distribution of the recording layer decreases the stability. Exchange interaction between recording layer and soft magnetic underlayer (SUL) scarcely affects the stability. Anisotropy field of SUL does not affect the stability. (C) 2006 American Institute of Physics.
Scientific journal, English - Current-induced magnetic vortex motion by spin-transfer torque
J Shibata; Y Nakatani; G Tatara; H Kohno; Y Otani
PHYSICAL REVIEW B, AMER PHYSICAL SOC, 73, 2, 020403(R), Jan. 2006, Peer-reviwed, We investigate the dynamics of a magnetic vortex driven by spin-transfer torque due to spin current in the adiabatic case. The vortex core represented by collective coordinate experiences a transverse force proportional to the product of spin current and gyrovector, which can be interpreted as the geometric force determined by topological charges. We show that this force is just a reaction force of Lorentz-type force from the spin current of conduction electrons. Based on our analyses, we propose analytically and numerically a possible experiment to check the vortex displacement by spin current in the case of single magnetic nanodot.
Scientific journal, English - Magnetic cluster formation in perpendicular thin films
H. Endo; Y. Uesaka; Y. Nakatani; N. Hayashi; H. Fukushima
INTERMAG 2006 - IEEE International Magnetics Conference, 944, 2006, Peer-reviwed
International conference proceedings, English - Dispersion effect of size, exchange and anisotropy of perpendicular media on read/write properties
Y. Nakatani; Y. Uesaka
INTERMAG 2006 - IEEE International Magnetics Conference, 698, 2006, Peer-reviwed
International conference proceedings, English - Effect of grain size on cluster size
H Endo; Y Uesaka; Y Nakatani; N Hayashi; H Fukushima
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 97, 10, pp. 10E312, May 2005, Peer-reviwed, A cluster size of a perpendicular medium was calculated from the correlation between grains in M-H loops. The cluster size was affected by physical properties as follows. When grain size is small and exchange stiffness constant A is not zero, the cluster size increases with decreasing grain-size. The increment of the cluster size decreases with increasing grain size distribution. The cluster size divided by the average grain size (normalized cluster size) increases with an increasing intergranular exchange coupling constant h(e) The normalized cluster size can be estimated from the grain-size distribution and the intergranular exchange coupling constant. (c) 2005 American Institute of Physics.
Scientific journal, English - Head-to-head domain walls in soft nano-strips: a refined phase diagram
Y Nakatani; A Thiaville; J Miltat
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, ELSEVIER SCIENCE BV, 290, 750-753, Apr. 2005, Peer-reviwed, The wall structure phase diagram in nano-strips is established by numerical calculations, exhibiting a hitherto unknown wall type, the asymmetric transverse wall. The diagram of the wall-width parameter is obtained both from a one-dimensional fit of the wall structure and from the domain wall motion velocity under field, the latter being more relevant to experiments. These two estimates show some differences, which are understood using the definition of the effective wall width proposed by Thiele. (c) 2004 Elsevier B.V. All rights reserved.
Scientific journal, English - Magnetization reversal below the Stoner-Wohlfarth field
H Fukushima; Y Uesaka; Y Nakatani; N Hayashi
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, ELSEVIER SCIENCE BV, 290, 526-529, Apr. 2005, Peer-reviwed, A novel concept of the critical switching field for the magnetization reversal of a single-domain particle with small damping constant in a field at an oblique angle to the easy axis is proposed. It is derived from the locus of the magnetization plotted on the contour map of the potential. The critical field is defined as the field in which the potential at the initial point is the same as that at the saddle point of the potential. The influence of the coordinate system on the critical field is also presented. (c) 2004 Elsevier B.V. All rights reserved.
Scientific journal, English - Micromagnetic understanding of current-driven domain wall motion in patterned nanowires
A Thiaville; Y Nakatani; J Miltat; Y Suzuki
EUROPHYSICS LETTERS, EDP SCIENCES S A, 69, 6, 990-996, Mar. 2005, Peer-reviwed, In order to explain recent experiments reporting a motion of magnetic domain walls (DW) in nanowires carrying a current, we propose a modi. cation of the spin transfer torque term in the Landau-Lifchitz-Gilbert equation. We show that it explains, with reasonable parameters, the measured DW velocities as well as the variation of DW propagation field under current. We also introduce coercivity by considering rough wires. This leads to a finite DW propagation field and finite threshold current for DW propagation, hence we conclude that threshold currents are extrinsic. Some possible models that support this new term are discussed.
Scientific journal, English - 電流による磁壁駆動 (Review)
多々良源; 河野浩; 柴田絢也; 仲谷栄伸; 山口明啓; 小野輝男
応用物理 ,74巻、12号 ,1598, 2005
Scientific journal, Japanese - Domain wall motion by spin-polarized current: a micromagnetic study
A Thiaville; Y Nakatani; J Miltat; N Vernier
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 95, 11, 7049-7051, Jun. 2004, Peer-reviwed, The effect of a spin-polarized current crossing a domain wall in a thin and narrow Permalloy(TM) strip is studied by micromagnetic simulations, supported by a one-dimensional model of wall dynamics. We use the simplest way to incorporate the spin-polarized current effect in the micromagnetic formalism; namely, a local momentum transfer under the assumption that the current polarization is in local equilibrium. We predict current influence on wall velocity and mobility under field. However, in order to reach agreement with recent experiments, more than ten times larger currents would be required within this simplest model. Thus, more elaborate models of spin transfer are needed. (C) 2004 American Institute of Physics.
Scientific journal, English - Effects of damping constant and gyromagnetic term on switching time of single-domain particle
H Fukushima; Y Uesaka; Y Nakatani; N Hayashi
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, ELSEVIER SCIENCE BV, 272, 745-746, May 2004, Peer-reviwed, The switching time of a single-domain particle with uniaxial anisotropy in a field at an oblique angle, a few degrees, to the easy axis is investigated by integrating numerically Brown's Fokker-Planck equation. The switching time calculated from the equation without gyromagnetic term is also presented to show the effect of the term. (C) 2003 Elsevier B.V. All rights reserved.
Scientific journal, English - Effects of exchange interaction and grain size distribution on cluster size in perpendicular media
H Endo; Y Uesaka; Y Nakatani; N Hayashi; H Fukushima
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, ELSEVIER SCIENCE BV, 272, 711-712, May 2004, Peer-reviwed, Computer simulation was used to investigate the effects of exchange interaction between adjacent grains and grain size distribution on cluster size of perpendicular magnetic recording media. The cluster size was determined from the correlation in the remanent magnetization state (M-r = 0) in the M-r-H loop. The cluster size increases with increasing exchange interaction, but it decreases with increasing grain size distribution. Exchange interaction between grains call be obtained from cluster size, grain size distribution, saturation magnetization,anisotropy field, average grain size, and temperature. (C) 2003 Elsevier B.V. All rights reserved.
Scientific journal, English - Measurement of Easy Axis Distribution
SANGUU T.; ENDO H.; UESAKA Y.; NAKATANI Y.; HAYASHI N.; FUKUSHIMA H.
Journal of the Magnetics Society of Japan, The Magnetics Society of Japan, 28, 3, 271-274, 01 Mar. 2004, We used computer simulation to examine an measuring method for easy axis distribution of a recording medium. Remanent magnetization Mr with the field applied in-plane showed that in-plane Mr increases with saturation magnetization Ms when the easy axis distribution is not random in plane, though Mr scarcely changes with Ms when the easy axis distribution is random in plane. We found that easy axis distribution perpendicular to the film plane does not affect in-plane Mr with the field applied in plane. We also found that easy axis distribution perpendicular to the film plane can be estimated from distribution of easy axis in plane, tilted direction of easy axis from the film plane, and perpendicular component of Mr with the field applied out of plane. Good agreements were obtained between experimentally derived remanent magnetization of VTR and audio tapes with the field applied out of plane and Mr derived from computer simulation.
Japanese - Influence of gyromagnetic term and temperature on switching time of a single-domain particle
H Fukushima; Y Uesaka; Y Nakatani; N Hayashi
IEEE TRANSACTIONS ON MAGNETICS, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 39, 5, 2519-2521, Sep. 2003, Peer-reviwed, Switching times of a single-domain particle with uniaxial anisotropy in an applied field at an oblique angle, a few degrees, to the easy axis were calculated as a function of applied field by solving Brown's Fokker-Planck equation numerically. The terms in the equation can be classified into three types: dissipative, gyromagnetic, and thermal. The influence of the term of each type on the switching time was studied.
Scientific journal, English - Faster magnetic walls in rough wires
Y Nakatani; A Thiaville; J Miltat
NATURE MATERIALS, NATURE PUBLISHING GROUP, 2, 8, 521-523, Aug. 2003, Peer-reviwed, True, In some magnetic devices that have been proposed, the information is transmitted along a magnetic wire of submicrometre width by domain wall (DW) motion. The speed of the device is obviously linked to the DW velocity, and measured values up to 1 km x s(-1) have been reported in moderate fields. Although such velocities were already reached in orthoferrite crystal films with a high anisotropy, the surprise came from their observation in the low-anisotropy permalloy. We have studied, by numerical simulation, the DW propagation in such samples, and observed a very counter-intuitive behaviour. For perfect samples (no edge roughness), the calculated velocity increased with field up to a threshold, beyond which it abruptly decreased--a well-known phenomenon. However, for rough strip edges, the velocity breakdown was found to be suppressed. We explain this phenomenon, and propose that roughness should rather be engineered than avoided when fabricating nanostructures for DW propagation.
Scientific journal, English - Computer simulations of magnetization switching of elongated magnetic particles with shape defects
H Endo; Y Uesaka; Y Nakatani; N Hayashi; H Fukushima
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 93, 12, 9865-9868, Jun. 2003, Peer-reviwed, The switching fields of elongated magnetic particles with various shape defects were investigated by means of computer simulations. The magnetic particles were approximated by rectangular parallelepipeds that have groove or chip defects. We modeled 13 types of particle shape defects for two particle sizes. The particle sizes used were "small particle" 10 nmx10 nmx50 nm and "large particle" 40 nmx40 nmx200 nm. The magnetocrystalline anisotropy field in the magnetic particles was set to zero. The switching fields of the small and large particles were found to decrease with the number of groove defects, but they were independent of the total number of chip defects. The magnetic moments of all of the small particles rotated almost coherently. The switching fields of the small particles almost coincided with the average of the difference between the demagnetizing fields in all cells along two directions: An easy-axis direction and one of the hard-axis directions. That is, we obtained the switching fields with various shapes from the demagnetizing fields even when the particles were deformed by defects. On the other hand, the magnetic moments of all the large particles rotated incoherently. The magnetic moments began to switch at particular planes that include the cell with the lowest difference between the demagnetizing fields in the easy-axis direction and one of the hard-axis directions. (C) 2003 American Institute of Physics.
Scientific journal, English - Effect of anisotropy field of soft magnetic underlayer on read/write properties in perpendicular recording media
Y Nakatani; N Hayashi; Y Uesaka; H Fukushima
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 93, 10, 7744-7746, May 2003, Peer-reviwed, The change in the read/write properties of double-layered perpendicular recording media with uniaxial anisotropy in the soft layer was investigated by micromagnetic simulation. It was found from the result of calculation that the media signal-to-noise ratio decreases by the soft layers, however, it can be improved by giving larger anisotropy to the soft layer. (C) 2003 American Institute of Physics.
Scientific journal, English - Remanent head field study of single pole-type head based on micromagnetics
M Mochizuki; C Ishikawa; H Ide; K Nakamoto; Y Nakatani; N Hayashi
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 93, 10, 6748-6750, May 2003, Peer-reviwed, The magnetization configurations within the pole tip of the single-pole-type head have been examined through a micromagnetic computer simulation based on the Landau-Lifshitz-Gilbert equation. The aspect ratio, including the effect of the exchange length (L-ex), was defined as the ratio of the throat height (T-h) to the write-track width (T-ww) and the thickness (T-p), which is given (T(h)xL(ex))/(T(ww)xT(p)). It was found that the magnetization configuration and the perpendicular component of remanent head field (Hr) are strongly dominated by this aspect ratio at any value of T-ww. It was also found that there is a characteristic aspect ratio at which Hr starts to decrease. These results show that decreasing the aspect ratio is an effective way to reduce the intensity of the remanent head field. (C) 2003 American Institute of Physics.
Scientific journal, English - Accuracy of the backward-difference solution of the Landau-Lifshitz-Gilbert equation
N Hayashi; Y Nakatani; Y Uesaka
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, INST PURE APPLIED PHYSICS, 42, 3, 1250-1257, Mar. 2003, Peer-reviwed, The reason for the low time-step accuracy of the previously developed approximate backward-difference solution of the Landau-Lifshitz-Gilbert (LLG) equation was found, and improved methods were developed. The improvement was carried out in two steps: correction of the expansion coefficients for the first-order backward-difference treatment of magnetization, and extension of the corrected scheme to a strict Crank-Nicolson scheme based on Newton's iteration. The time-step dependence of the velocity of a Bloch wall in planar- and perpendicular-magnetization films and the switching time of a fine iron-oxide particle were calculated to examine the time-step accuracy of the derived programs. The time-step dependence decreased considerably in the solutions obtained by the corrected program except for the Bloch wall motion in a perpendicular-magnetization film. However, it was removed almost entirely in the solutions obtained by the Crank-Nicolson method in which. Newton's iteration was repeated twice per time step.
Scientific journal, English - Analysis of MAMMOS Readout from Crescent Domains Using a Blue Laser
IMAI Susumu; NAKATANI Yoshinobu; AWANO Hiroyuki; ISHIZAKI Osamu; OTA Norio
Journal of the Magnetics Society of Japan, The Magnetics Society of Japan (MSJ), 2, 4, 297-299, 01 Oct. 2002, In the ongoing effort to achieve ultra high density Magneto-Optical recording, Laser Pumped Magnetic Field Modulation (LP-MFM) and Magnetic Amplifying Magneto-Optical System (MAMMOS) are considered promising methods. Using LP-MFM, crescent domains are recorded in a recording layer. Micro-magnetic simulations for the MAMMOS readout have already been reported assuming a crescent domain and red laser irradiation. Huth's equation simulations for the MAMMOS readout have also been reported assuming a circular recorded domain and blue laser irradiation. Micro-magnetic simulations for the MAMMOS readout assuming a blue laser irradiation, however, have not so far been reported. This paper presents the analysis of the combination of a 405nm blue laser and the MAMMOS readout from crescent recorded domains using the micro-magnetic simulations. In this work, MAMMOS readout from a crescent recorded domain is shown to be possible even with blue laser irradiation.
English - Dependence of switching time on temperature, applied field, and material parameters
H Fukushima; Y Uesaka; Y Nakatani; N Hayashi
IEEE TRANSACTIONS ON MAGNETICS, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 38, 5, 2394-2396, Sep. 2002, Peer-reviwed, The switching time of a single-domain particle with uniaxial anisotropy subjected to an applied field along the easy axis is studied by solving Brown's Fokker-Planck equation numerically. The equation is modified in order to be integrated by a finite-difference method. The validity of this method is verified by comparing the frequency prefactors in the exponential decay calculated by this method with the values from Brown's formula for the prefactor. Switching times for several values of the applied field and the temperature are calculated. Curves of the inverse of the switching time are fitted to a simple expression by using a least-squares method. The expression consists of two terms: a linear function of the applied field and a function proportional to the square root of the temperature. The dependence of the switching time on the magnetization, the volume of the particle, the anisotropy field, the Gilbert's damping constant, and the gyromagnetic constant is also presented.
Scientific journal, English - Effect of exchange interaction between grains on R/W properties of single-layer perpendicular recording media
Y Uesaka; H Endo; Y Nakatani; N Hayashi; H Fukushima
IEEE TRANSACTIONS ON MAGNETICS, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 38, 5, 2033-2035, Sep. 2002, Peer-reviwed, The effect of exchange interaction A between grains on signal (S) and signal-to-noise (S/N) ratio of single-layer perpendicular recording media was investigated by computer simulation. Oscillation of S and S/N, which could be due to the model of the media, was observed with the variation of head field. The maximum values of S (to be called S-max) and S/N (to be called S/N-max) in oscillation increase with increasing A in a small A range, saturate and decrease in a large A range. On the other hand, the minimum S and minimum S/N (to be called S-min and S/N-min) in oscillation decrease monotonically with increasing A. The value of A corresponding to the maximum of S/N-max in a A-S/N-max curve increases with increasing anisotropy field of a medium and decreases with increasing recording density. The S-max or S/N-max in oscillation may correspond to S and S/N of media with small grains or amorphous substances and S-min or S/N-min may correspond to S and S/N of media with large grains, respectively. Therefore, S and S/N of the media composed of small grains or amorphous substances with high H-k could be increased with increasing A.
Scientific journal, English - Thermal stability of written bits in double-layered perpendicular recording media
Y Nakatani; N Hayashi; Y Uesaka; H Fukushima
IEEE TRANSACTIONS ON MAGNETICS, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 38, 5, 2036-2038, Sep. 2002, Peer-reviwed, The thermal stability of written bits on single- and double- layered perpendicular magnetic recording media were compared from micromagnetic simulation. It was found that, although double-layered media shows a higher thermal stability than the single-layered media, the difference is not large. Under the calculation conditions used here the gain in thermal stability by double-layering was found to correspond to 7.5% increase in the volume of a magnetic grain. It was also found that this difference tends to decrease at the low and high ends of recording density. Investigation of the magnetostatic field exerted in the recording layer shows that the change in the thermal stability is due to the change in the layer-thickness component of the static field exerted on the recording layer. Although the increase in the dispersion in the easy axes of magnetization was found to decrease thermal stability, the decrease was greater in single-layered films than double-layered films.
Scientific journal, English - Effect of grain size dispersion on read/write properties in antiferromagnetically coupled recording media affected by thermal fluctuation
Y Nakatani; N Hayashi; Y Uesaka; H Fukushima
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 91, 10, 7691-7693, May 2002, Peer-reviwed, The effect of thermal fluctuation and grain-size dispersion on double-layered antiferromagnetically coupled (AFC) magnetic recording media is investigated by micromagnetic computer simulation. Calculations performed to obtain read/write properties show that the value of the underlayer saturation magnetization which yields maximum signal to noise ratio (SNR) is almost independent of the grain-size dispersion. The difference between the SNRs of the conventional and the AFC media was found not to depend on the grain-size dispersion but to be determined from other parameters such as the interlayer exchange constant, when the grains of both media are distributed with the same size dispersion. Thermal stability achieved by AFC was found to increase with increasing the interlayer exchange constant though the stabilization effect was seen to decrease as the grain-size dispersion is increased. (C) 2002 American Institute of Physics.
Scientific journal, English - Numerical solutions of the Fokker-Planck equation by the finite difference method for the thermally assisted reversal of the magnetization in a single-domain particle
H Fukushima; Y Uesaka; Y Nakatani; N Hayashi
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, ELSEVIER SCIENCE BV, 242, 1002-1004, Apr. 2002, Peer-reviwed, For an applied field at an oblique angle. a few degrees, to the easy axis it is shogun that a truncated Fourier series expansion can be an approximate solution to the Fokker Planck equation. Attempt frequency and switching time were calculated under different conditions. For an applied field along the easy axis an integral function is introduced to solve accurately. (C) 2002 Elsevier Science B.V. All rights reserved.
Scientific journal, English - Thermal stability of written bits in AFC recording media
Y Nakatani; N Hayashi; Y Uesaka; H Fukushima
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, ELSEVIER SCIENCE BV, 242, 409-412, Apr. 2002, Peer-reviwed, The influence of the material constants of the underlayer on the thermal stability of antiferromagnetically coupled recording media was investigated by micromagnetic computer simulation to derive combinations among the material parameters of the underlayer and the effective inter-layer exchange constant A which maximized the thermal stability. A simple formula is proposed which fits the derived relation between A and thermal stability. (C) 2002 Elsevier Science B.V. All rights reserved.
Scientific journal, English - Effect of material parameters of underlayer on read/write properties of AFC recording media
Y Nakatani; N Hayashi; Y Uesaka; H Fukushima
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, ELSEVIER SCIENCE BV, 242, 405-408, Apr. 2002, Peer-reviwed, The dependence of the saturation magnetization of the underlayer which maximizes the signal-to-noise ratio on the exchange coupling in the anti ferromagnetically coupled double-layered medium was investigated using micromagnetic computer simulation. The SNR was found to increase with increasing the inter-layer coupling until it decreased when the coupling constant exceeded beyond the optirnurn value. (C) 2002 Elsevier Science B.V. All rights reserved.
Scientific journal, English - Numerical simulation of switching time of magnetic particle
Y Uesaka; H Endo; T Takahashi; Y Nakatani; N Hayashi; H Fukushima
PHYSICA STATUS SOLIDI A-APPLIED RESEARCH, WILEY-V C H VERLAG GMBH, 189, 3, 1023-1027, Feb. 2002, Peer-reviwed, The effects of magnitude and angle of applied field and the effect of Gilbert damping constant on switching time of a cubic particle with crystalline anisotropy at 0 and 350 K were investigated by using numerical simulation. The switching time decreases with increasing angle of applied field at 0 and 350 K. The switching time is proportional to (1 + alpha(2))/alpha, when applied field is a few per cent larger than the Stoner-Wohlfarth switching field, and it is not proportional to (1 + alpha(2))/alpha when the applied field is close to the switching field. When the applied field is almost oriented in the -z direction, t(s) is proportinal to 1/((H/H-s) - 1). However, when the field is applied in the direction larger than a few degrees, t(s) is not proportional to 1/((H/H-s) - 1). Higher frequency than 1 GHz may be hard to be applied in perpendicular recording if the angle between the head field and the direction perpendicular to the film plane is smaller than a few degrees.
Scientific journal, English - Dependence of switching time on temperature
H. Fukushima; Y. Uesaka; Y. Nakatani; N. Hayashi
INTERMAG Europe 2002 - IEEE International Magnetics Conference, Institute of Electrical and Electronics Engineers Inc., 2002, Peer-reviwed, Switching times of a single-domain particle with uniaxial anisotropy were calculated under axially symmetric conditions by means of a numerical solution of Brown's Fokker-Planck equation with a finite difference method. The material parameters used were: magnetization Ms=300 emu/cm3, volume v=10-18 cm3, anisotropy field Hk=104 Oe and Gilbert's damping constant α=0.1. Initially the angles of the magnetization direction were distributed according to a Boltzmann distribution with an applied field H directed to the +z direction. Then the applied field was reversed to the -z direction. The switching time ts is defined as the time when the integral of the probability density over θ from 90° to 180° becomes 0.5.
International conference proceedings, English - Micro magnetic mechanism and comparison of domain expansion MO schemes toward 100 Gbit/in2
H. Awano; Y. Nakatani; S. Imai; M. Tani; M. Sekine; N. Ota
2002 International Symposium on Optical Memory and Optical Data Storage Topical Meeting, ISOM/ODS 2002 - Joint International Symposium on Optical Memory and Optical Data Storage 2002, Technical Digest, Institute of Electrical and Electronics Engineers Inc., 39-41, 2002, Peer-reviwed, To obtain an areal density of 100 Gbit/in2, magneto-optical (MO) technologies are attractive from the perspectives of magnetic field modulation recording, magnetic domain expansion readout, and high read/write cyclability. In this paper, we discuss the micro magnetic mechanism and compare the domain expansion MO schemes.
International conference proceedings, English - Read/write properties of oriented longitudinal recording media
Y Uesaka; Y Nakatani; N Hayashi; H Fukushima
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, ELSEVIER SCIENCE BV, 235, 1-3, 445-449, Oct. 2001, Peer-reviwed, The effect of orientation on the maximum recording density including the thermal stability effect was investigated using computer simulation. The necessary head current for a highly oriented medium is at most 10% larger than that for a 2D random medium. A recording density larger than 300 Gb/in(2) can be achieved with highly oriented media with 30nm flying height. (C) 2001 Elsevier Science B.V. All rights reserved.
Scientific journal, English - Magnetization reversal and electric transport in ferromagnetic nanowires
T Ono; Y Ooka; S Kasai; H Miyajima; Y Nakatani; N Hayashi; K Shigeto; K Mibu; T Shinjo
MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY, ELSEVIER SCIENCE SA, 84, 1-2, 126-132, Jul. 2001, Peer-reviwed, A method for magnetization reversal measurements in submicron magnetic wires was developed by utilizing the giant magnetoresistance effect, which enables us to determine a domain wall position as ii function of time, and allows to evaluate the propagation velocity of the domain wall easily. It was found that the magnetization reversal in a wire occurs in association with the propagation of a single domain wall and that an artificial neck introduced into the wire :acts as a pinning site of the magnetic domain wall. Injection of the magnetic domain wall from one end of the wire is demonstrated. Results on electric resistance measurements down to 20 mK for ultranarrow Ni wires are also presented. An increase of resistance proportional to T (1 2) was observed in a temperature range from 10 K to 80 mK. The result is discussed in terms of the electron -electron on interaction and the weak localization effects. (C) 2001 Elsevier Science B.V. All rights reserved.
Scientific journal, English - Computer simulation of domain wall motion in a magnetic strip line with submicron width
Y Nakatani; N Hayashi; T Ono; H Miyajima
IEEE TRANSACTIONS ON MAGNETICS, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 37, 4, 2129-2131, Jul. 2001, Peer-reviwed, The dynamics of magnetization reversal in a very narrow ferromagnetic wire was investigated by micromagnetic computer simulation. The calculation was performed both for an isolated finite-length wire and for an infinitely long wire which contained a domain wall in a portion. In the former calculation, a remanent equilibrium domain configuration was, at first, derived from a uniformly magnetized configuration. Then a reversal field was applied along the wire so as to nucleate and move the domain walls. A reversal field of a hundred and several tens Oe was necessary to nucleate a moving wall. It was found that the head of the moving wall had the shape of a wedge and that the wall dynamically changed its structure while moving. In the latter calculation, the mechanism of wall motion and the wall velocity at lower driving fields were evaluated. When the driving field was small enough, the wall moved with keeping its magnetic structure. The wall velocity became higher with increasing the width or decreasing the thickness of the wire. In the application of higher fields, however, the wall structure changed dynamically, and the wall velocity was almost twice as large as that in the steady-state motion.
Scientific journal, English - Time dependence of readout signal and media noise
Y Nakatani; N Hayashi; Y Uesaka; H Fukushima
IEEE TRANSACTIONS ON MAGNETICS, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 37, 4, 1544-1546, Jul. 2001, Peer-reviwed, The change with time in the readout signal and the media noise affected by thermal fluctuation was investigated by micromagnetic computer simulation. It was found that the logarithm of the time taken for the readout signal to decay by a constant factor was roughly in proportion to the value of KuV/T-k regardless of the presence or absence of the distribution in the grain size. The lines representing the logarithm of decay time against KuV/kT were almost parallel to each other when the decay factor was changed. It was found that the time dependence of the rate of the decay in the readout signal is similar to that of the rate of the increase in the media noise and that the change in the media noise preceded the change in the readout signal.
Scientific journal, English - Thermal stability in longitudinal thin film media
F. Akagi; M. Igarashi; K. Yoshida; Y. Nakatani; N. Hayashi
IEEE Transactions on Magnetics, 37, 4 I, 1534-1536, Jul. 2001, Peer-reviwed, Thermal stability in longitudinal thin film media was studied using a Monte-Carlo simulation. As recording densities increase, the signal decay ratios increase. The effect of the density is, however, very small. Between two materials with identified thermal stability factors 〈KuV〉/kT (where, Ku is the anisotropy constant, V is the volume of a grain, k is Boltzmann's constant, T is the temperature, and 〈〉 means an average value), the medium with smaller grains was found to be more stable against thermal fluctuations. These phenomena are related to the magnetic fields that are applied to grains in the media, which make the magnetzation stable against thermal fluctuation.
International conference proceedings, English - Micromagnetic simulation of wall motion for MAMMOS and DWDD
Y. Nakatani; N. Hayashi
J. Magn. Soc. Japan, The Magnetics Society of Japan, 25, 3, pp. 252-257-257, 2001, Peer-reviwed, The process of domain transcription and wall motion in magneto-optical recording media for MAMMOS and DWDD is investigated by micromagnetic computer simulation. The result of calculation agrees with experiment semiquantitatively, which shows the effectiveness of the micromagnetic simulation in the development of these devices.
English - Effect of thermal fluctuation on reversal field of magnetic fine particle with surface anisotropy
Y Nakatani; N Hayashi; Y Uesaka; H Fukushima; O Kitakami; Y Shimada
IEEE TRANSACTIONS ON MAGNETICS, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 36, 5, 3205-3207, Sep. 2000, Peer-reviwed, The magnetization reversal of a nanometer size ferromagnetic particle with surface anisotropy is investigated by micromagnetic computer simulation, Two kinds of calculations were performed: calculations with and without thermal fluctuation. In the case without thermal fluctuation a surface anisotropy of several ergs/cm(2) was found to increase the magnetization reversal field of the particle by a factor of ten as compared with the case without surface anisotropy, The introduction of surface anisotropy was also found to increase the reversal field, and hence, improve thermal stability.
Scientific journal, English - Effect of angle dependent attempt frequency on Arrhenius-Neel thermal decay in thin film media
M Igarashi; F Akagi; K Yoshida; Y Nakatani
IEEE TRANSACTIONS ON MAGNETICS, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 36, 5, 2459-2461, Sep. 2000, Peer-reviwed, The angle dependence of the attempt frequency f(o) has been determined by assuming isotropic thermal excitation in the anisotropic free energy around the easy axis of a singe-domain particle, The relationship between the logarithmic time and the time-dependent remanence coercivity N-cr was estimated. The acquired equation agrees well with the numerical calculation of the Langevin equation. The conventional formula do not give the correct relationship between H-cr and K-beta (= Kv/kT) because the exponent of K-beta depends on K-beta. The estimated K-beta from Sharrock's formula is 15% larger at K-beta of 100 and 5% smaller at K-beta of 50, Bertram's formula is effective at Ka of 100 but brings 7% smaller estimation at K-beta of 50.
Scientific journal, English - Micromagnetic Simulation of Wall Motion in Domain Wall Displacement Detection.
Kamata K.; Nakatani Y.; Shiratori T.; Kobayashi T.
Journal of the Magnetics Society of Japan, The Magnetics Society of Japan, 24, 9, pp. 1267-1270-1270, 2000, Peer-reviwed, A computer simulation of wall motion in domain wall displacement detection (DWDD) was performed using a micromagnetic model. The mechanism of the wall motion in the displacement layer and the effect of the track width and the defect of the track edge on the wall motion were investigated.
Japanese - Grain Size Dispersion Model of Magnetic Recording Media.
Oshima T.; Nakatani Y.
Journal of the Magnetics Society of Japan, The Magnetics Society of Japan, 24, 7, pp. 1157-1161-1161, 2000, Peer-reviwed, A grain size dispersion model for calculating the properties of magnetic recording media is proposed. The magnetic property and the read/write properties of several media were calculated by using this model and three previously proposed models to investigate the effect of the calculation model on the results. Simulation results show the validity of the proposed method.
Japanese - Effect of inter-granular exchange coupling on read/write properties in thin film recording media affected by thermal fluctuation
Y Nakatani; N Hayashi; Y Uesaka; H Fukushima
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 85, 8, 4726-4728, Apr. 1999, Peer-reviwed, The effect of thermal fluctuation and inter-granular exchange coupling on longitudinal and perpendicular magnetic recording media is investigated by computer simulation. It is found from the calculation of magnetic characteristics that the change in H-c due to thermal fluctuation can be suppressed by inter-granular exchange interaction in perpendicular recording media, but it can not be suppressed in longitudinal recording media. It is found from the calculation of read/write characteristics that magnetization states recorded in longitudinal recording media are affected by thermal fluctuation sooner with the increase in the inter-granular exchange coupling, while the magnetization states recorded in perpendicular recording media is found to become less sensitive to thermal effect when the inter-granular exchange coupling is increased. (C) 1999 American Institute of Physics. [S0021-8979(99)52208-1].
Scientific journal, English - Computer simulation of SNR in longitudinal and perpendicular recording
Y Uesaka; Y Nakatani; N Hayashi; H Fukushima
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, ELSEVIER SCIENCE BV, 193, 1-3, 399-405, Mar. 1999, Peer-reviwed, Magnetic properties, output signal, media noise and signal to noise ratio (SNR) in longitudinal and perpendicular magnetic recording at 350 K were investigated by solving the Langevin equation numerically and/or by using a Monte Carlo simulation. The exchange interaction between grains was assumed to be zero at first. The effect of thermal fluctuation on output signal of perpendicular media is smaller than that of longitudinal media when the thickness of the media is larger than the grain size, and it is opposite when the grain size is larger than the thickness. The maximum recording density was calculated assuming that SNR of 25 dB was necessary. For longitudinal recording, it is possible to attain the recording density of 30 Gb/in(2) after three years decay. For perpendicular recording, it is possible to attain the recording density of 50 Gb/in2 after three years decay. The signal increases and media noise decreases with increasing the exchange interaction between adjacent grains of perpendicular recording. (C) 1999 Elsevier Science B.V. All rights reserved.
Scientific journal, English - Physics of Domain Wall in Readout Layer of Magnetic Amplifying Magneto-Optical System
N. Hayashi; Y. Nakatani; H. Awano; N. Ohta
J. Magn. Soc. Jpn., The Magnetics Society of Japan, 23, 1, pp.151-156-156, 1999, Peer-reviwed, The results of two-dimensional dynamic calculations performed to simulate the domain transcription process in the readout layer of a magnetostatically coupled dual-layer magneto-optical recording medium and those of one-dimensional calculations made to clarify the nature of the domain wall in the readout layer are given. Detailed time-dependent magnetization behaviors in the readout layer are obtained in the former calculation showing the effect of various parameters such as the atmosphere temperature, stray fields from the recording layer and external fields, on domain transcription. The coercivity of the readout layer is realized by introducing dispersion into the magnitude of the anisotropy constant among computing cells, and the Landau-Lifshitz-Gilbert equation is solved numerically. The magnetization structures in a straight-line wall both in equilibrium and in motion are calculated in the latter calculation.
English - Accuracy of 45° tbrque method for obtaining anisotropy constant of 2D random films
Yasutaro Uesaka; Yoshinobu Nakatani; Hiroshi Fukushima; Nobuyuki Inaba
IEEE Transactions on Magnetics, 35, 5, 2673-2675, 1999, Peer-reviwed, Computer simulation was used to examine the accuracy of anisotropy energy constant, Ku, of thin film media obtained from the 45° torque method. The easy axes of the media were distributed randomly in plane. The obtained Ku value depends on range of the applied field. For 2D random media with HK = 1 ∼40 kOe, Ms = 100-600 emu/cm3, A=0-1 × 10-6 erg/cm, separation between adjacent grains=0-2 nm, the difference between obtained Ku value and exact Ku was at most 20%, if the range of applied field was larger than 10-20 kOe. Here, the standard values of the physical parameters were HK=10 kOe, Ms=460 emu/cm3, A=0, separation between adjacent grains = 0, and each parameter was varied successively. © 1999 IEEE.
Scientific journal, English - Influence of Damping Constant .ALPHA. on Recording Characteristics at High Frequencies.
Akagi F.; Igarashi M.; Yoshida K.; Nakatani Y.; Hayashi N.
Journal of the Magnetics Society of Japan, The Magnetics Society of Japan, 23, 4, pp. 1005-1008-1008, 1999, Peer-reviwed, The influence of the damping constant α on recording characteristics at high frequencies was simulated by using the Langevin equation, with the condition that the head field rise time is constant. In the frequency range up to 190 MHz the signal outputs for α = 1 and α = 0.05 are same. On the other hand, in the higher- frequency range over 190 MHz, where the head field decreases before it reaches the maximum value, the signal outputs for α = 0.05 are larger than those for α =1.0. This is because the critical switching field depends on the damping constant α and it decreases with a lower value of α.
Japanese - Effect of grain-size dispersion on read/write properties in thin film recording media affected by thermal fluctuation
Y Nakatani; N Hayashi; Y Uesaka; H Fukushima
IEEE TRANSACTIONS ON MAGNETICS, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 34, 4, 1618-1620, Jul. 1998, Peer-reviwed, The effect of thermal fluctuation and particle-size dispersion on longitudinal and perpendicular magnetic recording media is investigated by computer simulation. In the case of longitudinal recording media the coercive force depends largely on the size of the particle rather than its distribution while it depends on both particle size and its distribution in the case of perpendicular recording media. Calculations performed to obtain read/write properties show that removal of particle-size dispersion results in 92% and 229% increase in the recording density in the case of longitudinal and perpendicular recording media, respectively, when particle size is 120 Angstrom.
Scientific journal, English - Influence of Permanent Magnet Film Structures on the Read Characteristics of MR Heads
ISHIKAWA C.; TOTSUKA K.; IGARASHI M.; SUZUKI Y.; NAKATANI Y.; HAYASHI N.
Journal of the Magnetics Society of Japan, The Magnetics Society of Japan, 22, 4, 253-256, 15 Apr. 1998, The output fluctuations of magnetoresistive (MR) heads with abutted permanent magnets were analyzed by micro-magnetic simulation. The longitudinal bias field was calculated from the magnetization configuration of the permanent magnet (PM) film. The output fluctuation of the MR head was simulated by using the longitudinal bias field, which was calculated with various interface structures between the MR and PM films. When the PM film covered the track edge of the MR capping layer, the longitudinal bias field near the track edge was locally reduced. The local reduction of the bias field was caused by an extra field generated by a charge appearing at the edge of the region where the PM film overlaps the capping layer. It is proved that an MR head with a PM film covering the edge of the capping layer shows output fluctuation, whereas the output is stable when the PM film does not cover the capping layer.
Japanese - Volume average demagnetizing tensor of rectangular prisms
H Fukushima; Y Nakatani; N Hayashi
IEEE TRANSACTIONS ON MAGNETICS, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 34, 1, 193-198, Jan. 1998, Peer-reviwed, An exact analytic formula is presented for the magnetostatic field produced by a three-dimensional array of uniformly magnetized rectangular prisms, It is derived from the volume integration of a point-function demagnetizing tensor, The values of the point-function demagnetizing tensor at the centers of rectangular prisms of different aspect-ratios are compared with the volume averaged ones, This difference for the zz-component of demagnetizing tensors reaches 35% at its maximum when the aspect-ratio is 2.
Scientific journal, English - Monte Carlo simulation of thermal fluctuation in magnetization of longitudinal and perpendicular magnetic recording media
Y Uesaka; Y Takahashi; Y Nakatani; N Hayashi; H Fukushima
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, ELSEVIER SCIENCE BV, 174, 1-2, 203-218, Oct. 1997, Peer-reviwed, Thermal fluctuation in magnetization of longitudinal and perpendicular magnetic recording media was calculated using a Monte Carlo simulation method. Perpendicular recording is superior to longitudinal recording when the thickness is larger than the grain size. Longitudinal recording is superior to perpendicular recording when the grain size is larger than the thickness. Distribution of grain size increases thermal fluctuation of output signal of longitudinal and perpendicular recording media. In longitudinal recording, thermal fluctuation of the output signal increases with increasing recording density, but in perpendicular recording, it decreases with increasing recording density. In longitudinal recording, the reversal of magnetic moments begins near the transition region and then spreads to the other region, but in perpendicular recording the reversal of magnetic moments begins from the saturation region, In longitudinal recording media with well-oriented easy direction or in perpendicular recording media, the residual ratio of the output signal increases with increasing exchange interaction between adjacent grains, In longitudinal recording media in which the easy directions are in the plane of the media, but not well oriented, the residual ratio of the output signal decreases with increasing exchange interaction between adjacent grains when the interaction is not large (A < 0.4 x 10(-6) erg/cm), and increases with increase in the exchange interaction when it is large (A > 0.6 x 10(-6) erg/cm).
Scientific journal, English - Micromagnetic calculation of domain structure in thin magnetic film based on improved LaBonte method
N Hayashi; K Kosavisutte; Y Nakatani
IEEE TRANSACTIONS ON MAGNETICS, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 33, 5, 4164-4166, Sep. 1997, Peer-reviwed, A numerical method is developed to calculate equilibrium domain structures micromagnetically. The method is based on the LaBonte's iteration which is improved in such a way that the demagnetizing field is calculated simultaneously in advance of each iteration cycle and that a torque term which represents the gyroscopic nature of the magnetization is included in the update rule. The former modification allows the use of the fast Fourier transform (FFT) to calculate the demagnetizing field in the LaBonte method. The torque term is added to prevent the LaBonte's iteration from converging to a false solution different from that derived using the Landau-Lifshitz-Gilbert equation. The principle of calculation and the results of two-dimensional calculations which demonstrate the effectiveness of the developed method are presented.
Scientific journal, English - Simulation of MR response to transverse magnetic fields
K Fujimoto; K Totsuka; Y Uesaka; Saitoh, I; H Fukui; F Akagi; Yoshihara, I; Y Nakatani; N Hayashi
IEEE TRANSACTIONS ON MAGNETICS, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 33, 3, 2386-2391, May 1997, Peer-reviwed, The magnetoresistive (MR) response of an MR sensor with shields to a uniform applied field was calculated through a micromagnetic simulation, and the results were compared with those from an MR sensor without shields, A uniform longitudinal field, resulting from boundary pinning by exchange-biased antiferromagnetic films, was applied to the MR films of the two sensors. There are three differences between the MR sensors with and without shields: first, the slope of the MR response with shields near an applied field of zero is smaller than the slope of the response without shields, Second, the response of the shielded MR sensor has no subpeak, while the response of the unshielded MR sensor has a subpeak. Third, the output of the shielded MR sensor hardly decreases in a large field (1000 Oe), while the output of I:he unshielded MR sensor quickly falls to a small value in a field of 300 Oe. These differences are due to attenuated magnetic fields In the gap between the two shields except near the air bearing surface (ABS).
Scientific journal, English - Computer simulation of thermal fluctuation of fine particle magnetization based on Langevin equation
Y Nakatani; Y Uesaka; N Hayashi; H Fukushima
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, ELSEVIER SCIENCE BV, 168, 3, 347-351, Apr. 1997, Peer-reviwed, Thermal fluctuation after-effect is simulated using the Langevin equation. The relations between the number of reversals of a fine magnetic particle and the material parameters are investigated, and an experimental formula, p = 60 alpha/(1 + alpha(2)) exp((-k(u)v(0.979))/(kT)) is obtained for the transition probability due to the thermal fluctuation aftereffect. The formula is found to depend on the damping constant and the transition probability is 30 times as large as that predicted theoretically.
Scientific journal, English - Thermal stability of longitudinal and perpendicular recording media obtained by Monte Carlo simulation
Y Uesaka; Y Nakatani; N Hayashi; H Fukushima
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 81, 8, 4841-4841, Apr. 1997
English - Effect of thermal fluctuation on read/write properties of longitudinal and perpendicular recording media
Y Nakatani; N Hayashi; Y Uesaka; H Fukushima
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 81, 8, 4842-4842, Apr. 1997
English - Simulation of Thermal Fluctuation in Magnetizatoin of Longitudinal and Prependicular Recording Media with Grain Size Distribution
Y. Uesaka; Y. Nakatani; N. Hayashi; H. Fukushima
J. Mag. Soc. Jpn., 21, pp.277-282-282, 1997, Peer-reviwed - Calculation of demagnetizing field distribution based on fast Fourier transform of convolution
N Hayashi; K Saito; Y Nakatani
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, JAPAN J APPLIED PHYSICS, 35, 12A, 6065-6073, Dec. 1996, Peer-reviwed, It is confirmed that the calculation of the demagnetizing field in micromagnetic simulations can be accelerated significantly by using the discrete convolution theorem and the fast Fourier transform (FFT). When the magnetization distribution is periodic, application of the theorem to the demagnetizing field calculation is straightforward. Unlike the previously reported FFT method which is based on the continuous Fourier transform of the demagnetizing held, the method can also be used in the case of non-periodic magnetization structures. It is also confirmed that the result obtained using the new FFT method coincides with that of the conventional direct method, as expected. The principle of calculation and the results of one- and two-dimensional calculations which show the validity and effectiveness of the developed method are presented.
Scientific journal, English - Parallel Computation of a Demagnetizing Field in a Distributed Environment
Y. Nakatani
J. Mag. Soc. Japan, The Magnetics Society of Japan, 20, 1, pp. 35-40-40, 1996, Peer-reviwed, A parallel computation system for calculating a demagnetizing field in a distributed environment is presented. The system uses a hierarchically organized communication structure to reduce the time needed for communication between workstations. When 139 workstations were used, the total calculation speed was the same as that of a vector-type supercomputer with a computing speed of 1 GFLOPS.
English - Switching of single hexagonal particles with nonuniform magnetic properties
Y Uesaka; Y Nakatani; N Hayashi
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, JAPAN J APPLIED PHYSICS, 34, 11, 6056-6062, Nov. 1995, Peer-reviwed, Switching fields of hexagonal particles with nonuniform magnetic properties are investigated using computer simulation. The switching field of a hexagonal particle with a low anisotropy energy constant (K-u) region at a corner of all three thickness layers is lower than that of the uniform particle when the field is applied almost perpendicular to the hexagonal planet However, when the field is applied almost parallel to the hexagonal plane, the switching field of the nonuniform hexagonal particle is similar to that of the uniform particle. A hexagonal particle with a low K-u region at the center also switches in a lower field than the uniform particle does when the field is applied perpendicular to the hexagonal plane. The switching field of a hexagonal particle with low K-u region in the surface layer is almost the same as that of a uniform particle.
Scientific journal, English - METHOD OF MEASURING ANISOTROPY-FIELD OF A RECORDING MEDIUM INVESTIGATED BY COMPUTER-SIMULATION
Y UESAKA; T YOSHIDA; Y NAKATANI; N HAYASHI
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 77, 10, 5303-5308, May 1995, Peer-reviwed
Scientific journal, English - COMPUTER-SIMULATION OF MAGNETIZATION REVERSAL OF CUBIC, THIN AND ELONGATED PARTICLES - EFFECT OF METHOD OF CALCULATING DEMAGNETIZING FIELD
Y UESAKA; Y NAKATANI; N HAYASHI
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, ELSEVIER SCIENCE BV, 145, 1-2, 205-210, Mar. 1995, Peer-reviwed, Computer simulation was used to investigate the dependence of the switching fields and magnetization reversal mechanisms of cubic, thin and elongated particles on the angle of applied fields. In the simulation, the particles were divided or not divided into cells. The particles switch mostly in the coherent rotation mode. However, the switching field of the thin or elongated particle obtained by dividing the particle into cells does not coincide with the switching field of the particle obtained without dividing the particle into cells, except when a field is applied in the largest plane of a thin particle with the intrinsic uniaxial easy axis in the plane. The non-coincidence of the switching fields is due to the improper calculation method of the demagnetizing field. If the average demagnetizing fields, which are obtained by dividing the particles into cubic cells, are used in the undivided particle cases, the switching fields of the undivided particles coincide with the switching fields of the divided particles.
English - EFFECT OF DAMPING CONSTANT ON SWITCHING OF HEXAGONAL PLATELET PARTICLE
Y NAKATANI; N HAYASHI; Y UESAKA; H FUJIWARA
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, JAPAN J APPLIED PHYSICS, 33, 12A, 6546-6548, Dec. 1994, Peer-reviwed, The effect of Gilbert's damping constant alpha of a hexagonal platelet particle and the effect of the angle of the applied field on switching are investigated by computer simulation. The switching time decreases with the decrease of alpha in the range of 0.01 < alpha < 1 and becomes almost constant alpha < 0.01; the switching time is the time interval between the application of field and the earliest point at which the average magnetization in the easy direction becomes zero. The switching time decreases with the increase of the angle between the applied field and the easy direction. The oscillation amplitude of the average magnetization in the easy direction increases with the decrease of alpha, decreases with the increase of the presetting field, and increases with the increase of the angle between the applied field and the easy direction.
Scientific journal, English - INFLUENCE OF LONGITUDINAL BIAS FIELD ON MAGNETIZATION DISTRIBUTION IN MAGNETORESISTIVE HEAD WITH SHIELD FILMS
C ISHIKAWA; K SUZUKI; K YOSHIDA; Y SUGITA; K SHINAGAWA; Y NAKATANI; N HAYASHI
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 75, 2, 1036-1040, Jan. 1994, Peer-reviwed, The magnetization distribution in the magnetoresistive (MR) film has been calculated by self-consistently solving the three-dimensional field of the MR head. The magnetization distribution was calculated based on the Landau-Lifshitz-Gilbert equation and the head field was obtained by the Maxwell equation. The longitudinal bias field for the domain control was generated by exchange-coupled antiferromagnetic or permanent magnetic films which were formed outside the sensing region of the MR film. The resistance change of the MR film was calculated from the magnetization distribution with shield films and without shield films. It was found that the resistance change with the antiferromagnetic film without the shields was about two times larger than that with the permanent magnetic film with the remanence B-r of 0.7 T. The difference between them was reduced when the shields were formed because the stray field from the permanent magnetic film which is applied to the MR film was decreased by the shields. Further, the effect of the longitudinal bias field on the magnetization distribution was analyzed for the MR film without the shields. The influence of the antiferromagnetic film reached the region of 2-3 mu m from the end of the film, while that of the permanent magnetic film reached more than 10 mu m.
Scientific journal, English - COMPUTER-SIMULATION OF THIN-FILM MEDIA NOISE USING AN AUTOCORRELATION FUNCTION ALONG THE TRACK DIRECTION
K YOSHIDA; M HARA; Y UESAKA; Y NAKATANI; N HAYASHI
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 75, 2, 1190-1200, Jan. 1994, Peer-reviwed, The causes of thin-film media noise are discussed by deriving a formula which shows a direct relationship between the noise spectrum and the magnetization configuration of a thin-film medium. This formula is derived by Fourier-transforming the autocorrelation function of jM(x)-M(z) along the track direction, where M(x) and M(z) are the longitudinal and vertical components of magnetization, respectively. Noise and signal spectra are computed by means of this formula. The computed noise spectra are the maximum for a relatively long wavelength. Their form and intensity are shown to be strongly affected by the anisotropy constant and the axis orientation of easy magnetization.
Scientific journal, English - SIMULATION OF MAGNETIZATION DISTRIBUTION IN MAGNETORESISTIVE FILM UNDER A LONGITUDINAL BIAS FIELD
C ISHIKAWA; K SUZUKI; N KOYAMA; K YOSHIDA; Y SUGITA; K SHINAGAWA; Y NAKATANI; N HAYASHI
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 74, 9, 5666-5671, Nov. 1993, Peer-reviwed, The effects of longitudinal bias field, used for domain control on the magnetization distribution in a magnetoresistive (MR) film, have been investigated by computer simulation. The longitudinal bias field was generated by an exchange-coupled antiferromagnetic or permanent magnetic film formed on the MR film outside the sensing region. It was assumed that the magnetization in the part of the MR film on which the bias-generating films were formed was fixed along the easy axis. The spatial sensitivity of the MR film along the track width was evaluated by calculating the dependence of the resistance change on the position of a narrow track recording medium. It was found that the resistance change in the MR film with the anti-ferromagnetic film was roughly twice as large as the change in the film with the permanent magnetic film. The asymmetric sensitivity profile with respect to reflection about the track width mid-plane was also obtained. The asymmetry in the track sensitivity profile was found to be caused by three factors: asymmetric magnetization distribution about the track width mid-plane due to the transverse bias field, the difference in angular changes in the magnetization direction in the left and right regions facing the recording medium, and anisotropic flux propagation in the MR film.
Scientific journal, English - COMPUTER-SIMULATION OF ANNIHILATION PROCESS OF VERTICAL BLOCH LINE PAIR
Y NAKATANI; N HAYASHI
IEEE TRANSACTIONS ON MAGNETICS, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 29, 6, 2587-2589, Nov. 1993, Peer-reviwed, The annihilation process of a VBL pair caused by the injection of a BP, one of the processes proposed for VBL write function in the VBL memory, was investigated by micromagnetic calculation in three dimensions. The BP, which was nucleated on the film-top surface (near the write conductor) at the center of the VBL pair, was observed to move down inside the film while annihilating the VBL pair. When the current in the write conductor was large, the BP appeared not only on the film-top surface, but also within the film and on the film bottom surface.
Scientific journal, English - COMPUTATION OF SWITCHING FIELDS OF STACKED MAGNETIC HEXAGONAL PARTICLES WITH DIFFERENT HEIGHTS
Y UESAKA; Y NAKATANI; N HAYASHI
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, ELSEVIER SCIENCE BV, 124, 3, 341-346, Jun. 1993, Peer-reviwed, Switching fields of magnetic hexagonal particles with different heights, which were stacked in the easy axis direction, were investigated by computer simulation. The particles have easy axes perpendicular to their hexagonal planes. When the field is applied in the easy axis direction, the switching field of the stack is determined mainly by the end particle with the lowest switching field. On the other hand, when the field is applied in the hard axis direction, the switching field of the stack is mainly determined by the total height of the stack. The anisotropy field of a stack is also determined by the total height. The angular dependence of the switching field decreases with increasing number of stacked particles and with the total height of the stack. It also decreases when a small particle is stacked at one end of the stack.
Scientific journal, English - COMPUTER-SIMULATIONS OF SWITCHING FIELDS AND MAGNETIZATION REVERSAL MECHANISMS OF INTERACTING CUBIC PARTICLES - CASES WITH FIELDS APPLIED PARALLEL TO THE EASY AXES
Y UESAKA; Y NAKATANI; N HAYASHI
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, ELSEVIER SCIENCE BV, 123, 1-2, 209-218, May 1993, Peer-reviwed, Computer simulations were performed to investigate switching fields and magnetization reversal mechanisms of two, three, and four interacting cubic particles arranged in three configurations. The easy axes of all particles were oriented in the same direction, and fields were applied parallel to the easy axis. When three or four, particles are aligned in the hard axis direction, the magnetizations of the outer particles switch at a field lower than the field at which the center particle(s) switch(es). When the particles are aligned in the easy axis direction, the magnetizations of all the particles switch at the same field, but the magnetizations of the end particles switch faster than the magnetization of the center particle(s).
Scientific journal, English - COMPUTER-SIMULATIONS OF SWITCHING FIELDS AND MAGNETIZATION REVERSAL MECHANISMS OF INTERACTING CUBIC PARTICLES - CASES WITH FIELDS APPLIED PARALLEL TO THE EASY AXES
Y UESAKA; Y NAKATANI; N HAYASHI
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, ELSEVIER SCIENCE BV, 123, 1-2, 209-218, May 1993, Peer-reviwed, Computer simulations were performed to investigate switching fields and magnetization reversal mechanisms of two, three, and four interacting cubic particles arranged in three configurations. The easy axes of all particles were oriented in the same direction, and fields were applied parallel to the easy axis. When three or four, particles are aligned in the hard axis direction, the magnetizations of the outer particles switch at a field lower than the field at which the center particle(s) switch(es). When the particles are aligned in the easy axis direction, the magnetizations of all the particles switch at the same field, but the magnetizations of the end particles switch faster than the magnetization of the center particle(s).
Scientific journal, English - COMPUTER-SIMULATION OF MAGNETIZATION STATES IN A MAGNETIC THIN-FILM CONSISTING OF MAGNETOSTATICALLY COUPLED GRAINS WITH RANDOMLY ORIENTED CUBIC ANISOTROPY
O MURATA; K SAITO; Y NAKATANI; N HAYASHI
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 73, 10, 6513-6515, May 1993, Peer-reviwed, Computer simulations are performed to model the magnetically soft but isotropic behavior of an Fe-Si-Al alloy film. Solving the Landau-Lifshitz-Gilbert equation under the periodic boundary condition, magnetization states are simulated in a single layer film represented by a two-dimensional array of closely packed hexagonal prisms. Each prism represents a single crystal grain which is assumed to have randomly oriented cubic anisotropy and similar magnetic parameters as those of an Fe-Si-Al alloy film. It is also assumed that the magnetization is always uniform inside each grain and the exchange coupling among grains is zero. It is observed that the film without an external field shows a demagnetized state with considerably dispersed domain configuration where the characteristic wall and vortex structures are formed. It is also observed that the film is switched by applying an external field of which intensity depends on the cubic anisotropy constant of the grains. Analyzing the sum of exerting torque to the magnetization of grains, it is derived that the torque by cubic anisotropy is completely balanced with that by demagnetizing field.
Scientific journal, English - COMPUTER-SIMULATION OF SWITCHING FIELDS AND MAGNETIZATION STATES OF INTERACTING CUBIC PARTICLES - CASES WITH FIELDS APPLIED PARALLEL TO THE HARD AXES
Y UESAKA; Y NAKATANI; N HAYASHI
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, ELSEVIER SCIENCE BV, 123, 3, 337-358, May 1993, Peer-reviwed, Computer simulation was performed to investigate switching fields and magnetization states of an isolated, two, three, and four interacting cubic particles arranged in three kinds of configurations. The easy axes of the particles are oriented in the same directions, and the fields are applied parallel to the hard axis directions. Switching of magnetic moments occurs at fields near H(k) in all cases; large decreases (or an increase in one case) in the average magnetizations in the easy axis directions (z directions), M(z), occur at the switching fields. When a high field is applied in the hard axis direction (x direction) and reduced to zero, the magnetic moments of the particles form 180-degrees walls in the yz plane. The lowest switching field in each case is lower than H(k).
Scientific journal, English - S/N RATIO OF THIN-FILM MEDIA ESTIMATED BY COMPUTER-SIMULATION
K YOSHIDA; M HARA; Y UESAKA; Y NAKATANI; N HAYASHI
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 73, 10, 5578-5578, May 1993
English - MICROMAGNETIC COMPUTATION OF DAMPING CONSTANT EFFECT ON SWITCHING MECHANISM OF A HEXAGONAL PLATELET PARTICLE
Y UESAKA; Y NAKATANI; N HAYASHI
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, JAPAN J APPLIED PHYSICS, 32, 3A, 1101-1106, Mar. 1993, Peer-reviwed, The effect of Gilbert's damping constant on the switching mechanism of a magnetic hexagonal platelet particle was investigated by computer simulation. Three damping constants were used for the calculation: alpha = 1, 0.3 and 0.1. When a uniform field is applied in the direction of the easy axis of the platelet, the average magnetization in that direction begins to oscillate. The amplitude of the oscillation, which increases with decreasing damping constant, decreases with time. Switching occurs after the oscillation ceases. The magnetic moments of the platelets switch in the vortex mode for all damping constants investigated. The switching mechanism is complicated in a small a platelet; the center of the vortex moves around in a hexagonal plane at small alpha (alpha = 0.1), but the center of the vortex stays at the center at large alpha (alpha = 0.3, 1).
Scientific journal, English - COMPUTATION OF SWITCHING FIELDS OF STACKED MAGNETIC HEXAGONAL PLATELET PARTICLES
Y UESAKA; Y NAKATANI; N HAYASHI
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, ELSEVIER SCIENCE BV, 114, 1-2, 217-223, Aug. 1992, Peer-reviwed, Switching fields of magnetic hexagonal platelet particles, which were stacked to the easy axis directions, were investigated by computer simulation. The particles had the easy axes perpendicular to the hexagonal planes. The angular dependence of the switching fields became smaller when more particles were stacked and when the particles were stacked closer together. This result is considered as one of the reasons for the small angular dependence of the remanence coercivity of a longitudinally oriented barium ferrite medium. Absence of exchange interaction between adjacent layers in a particle also reduces the angular dependence of the switching field.
Scientific journal, English - DYNAMICAL CALCULATION OF MAGNETIZATION REVERSAL IN SMALL PARTICLES
UESAKA Yasutaro; NAKATANI Yoshinobu; HAYASHI Nobuo
ITE Technical Report, The Institute of Image Information and Television Engineers, 16, 44, 43-48, 1992, The Landau- Lifshitz-Gilbert (LLG) equation is solved to investigate the switching fields and magnetization reversal mechanisms of cubic, elongated, or hexagonal platelet particles. Squareness scarcely changes until the particle size exceeds a critical value. Some time interval is necessary for the irreversal transition to occur in each case. The switching fields and the magnetization reversal mechanisms of the particles change with the material parameters (size, exchange stiffness constant, anisotropy constant).
English - 2 INTERACTING CUBIC PARTICLES - EFFECT OF PLACEMENT ON SWITCHING FIELD AND MAGNETIZATION REVERSAL MECHANISM
GWD SPRATT; Y UESAKA; Y NAKATANI; N HAYASHI
IEEE TRANSACTIONS ON MAGNETICS, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 27, 6, 4790-4792, Nov. 1991, Peer-reviwed, The Landau-Lifshitz-Gilbert equation was used to investigate the effect of interparticle interactions on the remauent states and magnetisation reversal mechanisms of interacting cubic particles. The cubic particle had a uniaxial anisotropy constant in the z direction, K(uz), of 1.96 x 10(5) erg/cc. Interparticle interactions were varied by considering different placements of the second particle. Reversal mechanisms were determined at an applied field of 1.05 x switching field. The reversal mechanism of the isolated cubic particle was also determined.
Interparticle interactions were found to have a drastic effect on the switching field. Positive interactions were observed when the particles were separated in the z direction. The reversal mechanisms for the isolated particle and the positively interacting pair were very similar, despite a large difference in the switching field. When the particles were displaced in the x direction the switching field of the interacting pair was reduced from that of the isolated particle. The reversal mechanism for this particle configuration was very complex and asymmetric, due to the non-uniformity of the interaction field. An interesting feature was observed when the particles were separated in the x and z direction. The switching field for this arrangement was also lower than that of the isolated particle, indicating a net negative interaction effect. This simulation result may help to explain the experimental observation of net negative interactions for acicular particles.
Scientific journal, English - COMPUTER-SIMULATION OF MAGNETIZATION REVERSAL MECHANISMS OF HEXAGONAL PLATELET PARTICLE - EFFECT OF MATERIAL PARAMETERS
Y NAKATANI; N HAYASHI; Y UESAKA
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, JAPAN J APPLIED PHYSICS, 30, 10, 2503-2512, Oct. 1991, Peer-reviwed, The effect of material parameters on the switching mechanism and switching field, H(sw), of hexagonal platelet particles was investigated by computer simulation. The field H(E) was applied perpendicular to the platelet plane which is the easy axis direction of the platelet. The magnetic moments of platelets with a small exchange stiffness constant, A, switch in the normal vortex mode; those of particles with a large A switch in the quasi-coherent rotation mode. The magnetic moments of platelets with a small uniaxial anisotropy constant, K(u), reverse in the normal vortex mode; platelets with a large K(u) reverse in the crater mode. The magnetic moments of a thin platelet switch in the quasi-coherent rotation mode; a thick platelet switches in the normal vortex mode.
Scientific journal, English - MICROMAGNETIC CALCULATION OF APPLIED FIELD-EFFECT ON SWITCHING MECHANISM OF A HEXAGONAL PLATELET PARTICLE
Y UESAKA; Y NAKATANI; N HAYASHI
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, JAPAN J APPLIED PHYSICS, 30, 10, 2489-2502, Oct. 1991, Peer-reviwed, The effect of the applied field on the switching mechanism of a hexagonal platelet particle was investigated by computer simulation. The fields were applied perpendicular to the platelet plane which is the easy axis direction of the platelet. As the applied field increases, the switching mechanism changes from the normal vortex mode (in which the magnetic moments in a hexagonal plane rotate about the center of the plane, and the moments in the top and bottom planes rotate in the same direction) to the crater mode (in which the moments do not form a vortex, and the moments at the center of the hexagon switch faster than the moments at the corners), then to the quasi-coherent rotation mode and finally to the twisted vortex mode (in which the moments in the top and bottom planes rotate in opposite directions).
Scientific journal, English - ON THE INFLUENCE OF WALL MICRODEFORMATIONS ON BLOCH LINE VISIBILITY IN BUBBLE GARNETS
A THIAVILLE; J BENYOUSSEF; Y NAKATANI; J MILTAT
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 69, 8, 6090-6095, Apr. 1991, Peer-reviwed, It is proposed that the main source of contrast of vertical Bloch lines (VBLs) in bubble garnets, when viewed by means of anisotropic dark field optical imaging, is a microdeformation of the wall plane at line location. The motive force for wall tilting is the compensation of the monopolar sigma charges borne by VBLs. The tilted wall section acts as a phase object and allows for the formation of line images with well-defined symmetries and independent of the incident-beam polarization. All these features agree fully with experimental evidence. An approximate model of the wall deformation is presented and shown to be consistent for a given thickness and material parameters with the results of an ab initio numerical computation of the 3D structure of a VBL. The implications of the microdeformation model in terms of line observability are analyzed and compared with experimental data.
Scientific journal, English - COMPUTER-SIMULATION OF MAGNETIZATION REVERSAL - THE EFFECT OF SHAPE AND UNIAXIAL CRYSTALLINE ANISOTROPY
G SPRATT; Y UESAKA; Y NAKATANI; N HAYASHI
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 69, 8, 4850-4852, Apr. 1991, Peer-reviwed, The Landau-Lifshitz-Gilbert equation has been used to compare the hysteresis loops and magnetization-reversal mechanisms of a cubic particle, with uniaxial crystalline anisotropy, and a 2:1-aspect-ratio elongated particle. The switching fields of these particles were 700 Oe. The cubic particle exhibited a square hysteresis loop, but the elongated particle had a nonsquare hysteresis loop due to the tilting of spins in the surface layers. Magnetization reversal for the elongated particle was initiated at the surface layers. For the cubic particle the reversal was initiated at an edge of the particle and spread through to the central elements. Differences between the hysteresis loops and reversal mechanisms, for the different particles, are attributed to the different nature of the magnetic anisotropies.
Scientific journal, English - COMPUTER-SIMULATION OF MAGNETIZATION REVERSAL IN FINE HEXAGONAL PLATELET PARTICLES WITH DEFECTS
Y UESAKA; Y NAKATANI; N HAYASHI
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 69, 8, 4847-4849, Apr. 1991, Peer-reviwed, The Landau-Lifshitz-Gilbert equation is used to investigate the switching fields and mechanisms of fine hexagonal platelet particles which have three types of defects in comparison with a nondefect particle. Two of the defects are surface defects, one with an area more than 50% of the hexagon and the other much less than 50%. The third defect is not a surface defect but a defect which extends from the top to bottom surface. The differences between the switching fields of these particles are small, at most 12%. The angular dependence of the switching fields of these particles is similar to the ones derived from the coherent rotation mode. The switching mechanisms of the particles change with applied field. The nondefect particle switch in a normal vortex mode and the particles with defects switch in a mixture of normal vortex and coherent rotation-like mode at the applied field = H(sw) (switching field). Most of them switch in a twisted vortex mode at the applied field = 3 X H(sw). But in surface defect particles, whose defect area is more than 50% of the hexagon, the switching mechanism hardly changes from a coherent rotation-like mode.
Scientific journal, English - DYNAMIC CALCULATION OF MAGNETIZATION REVERSAL IN ELONGATED PARTICLES
Y UESAKA; Y NAKATANI; N HAYASHI
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 67, 9, 5146-5148, May 1990, Peer-reviwed
Scientific journal, English - COMPUTER-SIMULATION OF MAGNETIZATION REVERSAL IN FINE HEXAFERRITE PARTICLES
Y NAKATANI; Y UESAKA; N HAYASHI
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 67, 9, 5143-5145, May 1990, Peer-reviwed
Scientific journal, English - A Note on Deleting the Maximum Element in Nested S-Heap
K. Noshita; Y. Nakatani
Trans. on the IECE, E 73, pp. 1725-1726, 1990, Peer-reviwed - DIRECT SOLUTION OF THE LANDAU-LIFSHITZ-GILBERT EQUATION FOR MICROMAGNETICS
Y NAKATANI; Y UESAKA; N HAYASHI
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, JAPAN SOC APPLIED PHYSICS, 28, 12, 2485-2507, Dec. 1989, Peer-reviwed
Scientific journal, English - DIRECT SOLUTION OF LANDAU-LIFSHITZ-GILBERT EQUATION FOR DOMAIN-WALLS IN THIN PERMALLOY-FILMS
N HAYASHI; T INOUE; Y NAKATANI; H FUKUSHIMA
IEEE TRANSACTIONS ON MAGNETICS, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 24, 6, 3111-3113, Nov. 1988, Peer-reviwed
Scientific journal, English - 3-DIMENSION CALCULATION OF VERTICAL BLOCH LINE AND BLOCH POINT
Y NAKATANI; N HAYASHI
IEEE TRANSACTIONS ON MAGNETICS, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 24, 6, 3039-3041, Nov. 1988, Peer-reviwed
Scientific journal, English - NUMERICAL-SOLUTION OF LANDAU-LIFSHITZ-GILBERT EQUATION WITH 2 SPACE VARIABLES FOR VERTICAL BLOCH LINES
N HAYASHI; Y NAKATANI; T INOUE
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, JAPAN J APPLIED PHYSICS, 27, 3, 366-378, Mar. 1988, Peer-reviwed
Scientific journal, English - COMPUTER-SIMULATION OF TWO-DIMENSIONAL VERTICAL BLOCH LINES BY DIRECT INTEGRATION OF GILBERT EQUATION
Y NAKATANI; N HAYASHI
IEEE TRANSACTIONS ON MAGNETICS, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 23, 5, 2179-2181, Sep. 1987, Peer-reviwed
Scientific journal, English - Variational calculus for vertical bloch lines.
Nakatani Y.; Hayashi N.
Journal of the Magnetics Society of Japan, The Magnetics Society of Japan, 11, 2, pp. 133-138-138, 1987, Peer-reviwed, Magnetization distributions around vertical Bloch lines (VBL's) in the wall-center plane are calculated by direct minimization of the energy of the system. A successive approximation method using the Newton's method has been developed to solve the Euler equation numerically. The method has been found very effective to obtain equilibrium configurations in small iteration steps as compared with the dynamic calculation based on the so-called equation of wall motion. The calculation includes two-dimensional VBL's in which variations along the Z-axis are neglected and three-dimensional VBL's in which surface-to-surface magnetization twist is taken into consideration. Effective interaction field between two VBL's is calculated as a function of the VBL separation in both cases. The paper descibes the formulation of the problem, method of numerical calculation, and results.
Japanese - COMPUTER-SIMULATION OF MAGNETIC DOMAIN-WALL MOTION TO DERIVE EFFECTIVE INTERACTION FORCES BETWEEN VERTICAL BLOCH LINES
N HAYASHI; Y NAKATANI
IEEE TRANSACTIONS ON MAGNETICS, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 22, 5, 796-798, Sep. 1986, Peer-reviwed
Scientific journal, English - NUMERICAL-CALCULATION OF MAGNETIC-BUBBLE DOMAIN-WALL MOTION BASED ON A LUMPED-CONSTANT MODEL OF VERTICAL BLOCH LINES
N HAYASHI; Y NAKATANI
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, JAPAN J APPLIED PHYSICS, 25, 3, 406-418, Mar. 1986, Peer-reviwed
Scientific journal, English - COMPUTER-SIMULATION OF THE MOTION OF MAGNETIC DOMAIN-WALL BASED ON LUMPED-CONSTANT MODEL OF VERTICAL BLOCH LINES
N HAYASHI; Y NAKATANI
IEEE TRANSACTIONS ON MAGNETICS, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 21, 5, 1767-1769, 1985, Peer-reviwed
Scientific journal, English - A lumped-constant model of vertical Bloch lines.
Hayashi N.; Nakatani Y.
Journal of the Magnetics Society of Japan, The Magnetics Society of Japan, 9, 2, pp. 181-186-186, 1985, Peer-reviwed, A formulation has been developed in which the magnetization structure along a magnetic domain wall within a vertical Bloch line is regarded as packed into a single point on the wall, concentrated Bloch-line point. Equations of motion have been derived for the concentrated Bloch line from equations of wall motion developed previously for a two-dimensional wall which was regarded as a locus of domain-center points. Programs have been developed to solve the motion of a domain wall which is arbitrary in shape and contains arbitrary number of concentrated Bloch lines. The results of computer simulation made for bubbles and plane-like walls show the validity of the formulation and the numerical method. The new equations of motion for concentrated Bloch line have been found not to be as stiff as the conventional equations of wall motion in the case with Bloch lines. An outline of the formulation and the method of numerical solution are presented together with preliminary results of computer simulation.
Japanese - Lumped Constant and Distributed Models of Vertical Bloch Lines
N. Hayashi; Y. Nakatani
IEEE Translation Journal on Magnetics in Japan, 1, 9, 1148-1150, 1985, Peer-reviwed, The lumped constant model for vertical Bloch lines (in which a VBL is treated as a single point in the domain wall) is modified to take into account repulsive forces between VBLs and other factors, thereby making it as accurate as the conventional distributed VBL model. Simulations were performed based on the two models, for translational motion of a circular bubble with two VBL in the domain wall
the q value dependence of the skew angle, which does not appear in results for simple lumped constant models, is found in the results for the modified lumped constant model. © 1986 IEEE.
Scientific journal, English - Numerical Stability of Lumped Constant Model for VBL Dynamics
N. Hayashi; Y. Nakatani
IEEE Translation Journal on Magnetics in Japan, 1, 9, 1153-1154, 1985, Peer-reviwed, An implicit method is used to improve the stability of the numerical simulation of vertical Bloch line motion. In the equations of motion, VR, VS and φa are replaced by their respective changes per time increment ΔT. The values of the various force terms at a future time T + ΔT are estimated from their values at time T using appropriate correction terms, and a system of simultaneous linear equations in ΔR, Δφa and ΔS is obtained for each domain wall point. Whereas explicit solutions are numerically stable for ΔT as large as 0.2 ns, this implicit solution is stable for ΔT taken as large as 16 ns. © 1986 IEEE.
Scientific journal, English - Lumped Constant Model for VBL Pair
N. Hayashi; Y. Nakatani
IEEE Translation Journal on Magnetics in Japan, 1, 9, 1151-1152, 1985, Peer-reviwed, In addition to the usual lumped constant model for vertical Bloch lines, the authors introduce exchange repulsive forces acting between VBL, and processing to describe passing of normal domain wall points by VBL. Assumptions regarding φn and δφn are made for BL winding in the positive and negative directions, and an empirical formula for the repulsive force in terms of the VBL separation is derived from distributed VBL model simulations. The passing processing assumes normal domain wall points approached by VBL points to vanish, while at the same time new wall points are generated behind the VBL point. © 1986 IEEE.
Scientific journal, English - Computer Simulation of the Motion of a Domain Wall Containing Lumped—Constant Bloch Lines
N. Hayashi; Y. Nakatani
IEEE Translation Journal on Magnetics in Japan, 1, 2, 247-248, 1985, Peer-reviwed
Scientific journal, English
MISC
- Information Stability in Heat-Assisted Magnetic Recording
T. Kobayashi; Y. Nakatani; Y. Fujiwara
Dec. 2019, IEICE Technical Report, MRIS2019, 44, 41-46, Japanese, Summary national conference - Computer simulation of domain wall motion induced by a slope electric field.
S. Murayama; K. Yamada; Y. Nakatani
IEEE, 2015, 2015 IEEE MAGNETICS CONFERENCE (INTERMAG), English, Summary international conference, WOS:000381606001466 - 9pBF-5 Switching of a Magnetic Vortex Core in a Pac-man Disk using a Single Current Pulse
Yamada Keisuke; Sato Tomonori; Nakatani Yoshinobu
The Physical Society of Japan (JPS), 22 Aug. 2014, Meeting abstracts of the Physical Society of Japan, 69, 2, 309-309, Japanese, 1342-8349, 110009887305, AA11439205 - 9pBF-7 Domain wall dynamics in the presence of the Dzyaloshinskii-Moriya interaction
Yoshimura Yoko; Kim Kab-Jin; Taniguchi Takuya; Ueda Kohei; Hiramatsu Ryo; Moriyama Takahiro; Tanigawa Hironobu; Suzuki Tetsuhiro; Kariyada Eiji; Nakatani Yoshinobu; Ono Teruo
The Physical Society of Japan (JPS), 22 Aug. 2014, Meeting abstracts of the Physical Society of Japan, 69, 2, 310-310, Japanese, 1342-8349, 110009887307, AA11439205 - 28aAF-3 Observation of metastable bound state between domain walls in an asymmetric Co/Ni nanowire II
Hiramatsu R.; Kim Kab-Jin; Hata H.; Taniguchi T.; Tanigawa H.; Kariyada H.; Suzuki T.; Nakatani Y.; Moriyama T.; Ono T.
The Physical Society of Japan (JPS), 05 Mar. 2014, Meeting abstracts of the Physical Society of Japan, 69, 1, 510-510, Japanese, 1342-8349, 110009835391, AA11439205 - 28aAF-4 Switching of the Magnetic Vortex Core in a Pac-man Disk
Yamada Keisuke; Sato Tomonori; Nakatani Yoshinobu
The Physical Society of Japan (JPS), 05 Mar. 2014, Meeting abstracts of the Physical Society of Japan, 69, 1, 510-510, Japanese, 1342-8349, 110009835392, AA11439205 - Mechanism change of current-induced magnetic domain wall motion in multilayered Co/Ni nanowires
Ueda K.; Kim K-J.; Hiramatsu R.; Moriyama T.; Chiba D.; Tanigawa H.; Kariyada E.; Suzuki T.; Nakatani Y.; Ono T.
The Physical Society of Japan (JPS), 26 Aug. 2013, Meeting abstracts of the Physical Society of Japan, 68, 2, 367-367, Japanese, 1342-8349, 110009756557, AA11439205 - Switching of the Magnetic Vortex Core in Elliptical Disks by Nano-second Field Pulses
Yamada Keisuke; Sato Tomonori; Nakatani Yoshinobu; Kasai Shinya; Chiba Daichi; Kobayashi Kensuke; Thiaville Andre; Ono Teruo
The Physical Society of Japan (JPS), 26 Aug. 2013, Meeting abstracts of the Physical Society of Japan, 68, 2, 424-424, Japanese, 1342-8349, 110009756772, AA11439205 - Influence of spin Hall effect for current-induced domain wall motion in a perpendicularly magnetized Co/Ni nanowire
Yoshimura Y.; Koyama T.; Moriyama T.; Kim Kab-Jin; Chiba D.; Nakatani Y.; Fukami S.; Yamanouchi M.; Ohno H.; Ono T.
The Physical Society of Japan (JPS), 26 Aug. 2013, Meeting abstracts of the Physical Society of Japan, 68, 2, 415-415, Japanese, 1342-8349, 110009756743, AA11439205 - 27pXA-6 Current pulse width dependence of magnetic domain wall motion in the presence of bias magnetic field
Kim Kab-Jin; Chiba D.; Nakatani Y.; Fukami S.; Yamanouchi M.; Ohno H.; Ono T.
The Physical Society of Japan (JPS), 26 Mar. 2013, Meeting abstracts of the Physical Society of Japan, 68, 1, 540-540, English, 1342-8349, 110009644377, AA11439205 - 26aPS-18 Detection of magnetization rotation in domain wall induced by spin transfer torque in Co/Ni nanowire
Kim Kab-Jin
The Physical Society of Japan (JPS), 26 Mar. 2013, Meeting abstracts of the Physical Society of Japan, 68, 1, 502-502, Japanese, 1342-8349, 110009644237, AA11439205 - 26aPS-17 Current-induced domain wall motion in a perpendicularly magnetized Co/Ni nanowire under in-plane magnetic field (III)
Yoshimura Y; Koyama T; Moriyama T; Chiba D; Tanigawa H; Kariyada E; Suzuki T; Nakatani Y; Ono T
The Physical Society of Japan, 2013, Meeting Abstracts of the Physical Society of Japan, 68, 0, 502-502, Japanese, 1342-8349, 110009644236, AA11439205 - 27pXA-5 Temperature Dependence of Current-Induced Magnetic Domain Wall Motion in a Multilayered Co/Ni Nanowire with MgO Cap
上田 浩平; 小野 輝男; 平松 亮; キムカブジン; 森山 貴広; 千葉 大地; 谷川 博信; 苅屋田 英嗣; 鈴木 哲広; 仲谷 栄伸
The Physical Society of Japan, 2013, Meeting Abstracts of the Physical Society of Japan, 68, 0, 539-539, Japanese, 1342-8349, 110009644376, AA11439205 - 27aAA-9 Current-induced domain wall motion in a perpendicularly magnetized Co/Ni nanowire under in-plane magnetic field
Yoshimura Y; Koyama T; Chiba D; Fukami S; Yamanouchi M; Ohno H; Nakatani Y; Ono T
The Physical Society of Japan, 2012, Meeting Abstracts of the Physical Society of Japan, 67, 0, 533-533, Japanese, 1342-8349, 110009566778, AA11439205 - 27aAA-10 High-field motion of magnetic domain wall in (Co/Ni) nanostrips
Yamada K; Jamet Jean-Pierre; Nakatani Y; Ueda K; Mougin Alexandra; Thiaville Andre; Ono T; Ferre Jacques
The Physical Society of Japan, 2012, Meeting Abstracts of the Physical Society of Japan, 67, 0, 533-533, Japanese, 1342-8349, 110009566779, AA11439205 - 20aCC-10 Current-induced domain wall motion in a perpendicularly magnetized Co/Ni nanowire under in-plane magnetic field (II)
Yoshimura Y; Koyama T; Chiba D; Fukami S; Yamanouchi M; Ohno H; Nakatani Y; Ono T
The Physical Society of Japan, 2012, Meeting Abstracts of the Physical Society of Japan, 67, 0, 427-427, Japanese, 1342-8349, 110009600017, AA11439205 - 27aAA-8 Temperature Dependence of Spin Polarization of Current in Co/Ni Nanowire Estimated from Current-Induced Magnetic Domain Wall Motion
Ueda K; Nakatani Y; Ono T; Koyama T; Hiramatsu R; Chiba D; Fukami S; Tanigawa H; Suzuki T; Ohshima N; Ishiwata N
一般社団法人 日本物理学会, 2012, Meeting Abstracts of the Physical Society of Japan, 67, 0, 533-533, Japanese, 1342-8349, 110009566777, AA11439205 - 24aPS-28 Detection of magnetization rotation in domain wall induced by spin transfer torque
Hiramatsu R; Kondou K; Koyama T; Chiba D; Fukami S; Ishiwata N; Nakatani Y; Ono T
The Physical Society of Japan, 2012, Meeting Abstracts of the Physical Society of Japan, 67, 0, 481-481, Japanese, 1342-8349, 110009566582, AA11439205 - 24aPS-29 Additivity of magnetic domain wall velocities induced by current and field
Koyama T; Ueda K; Chiba D; Fukami S; Ishiwata N; Kohno H; Nakatani Y; Kobayashi K; Ono T
The Physical Society of Japan, 2012, Meeting Abstracts of the Physical Society of Japan, 67, 0, 481-481, Japanese, 1342-8349, 110009566583, AA11439205 - 27aAA-3 Manipulation of the vortex core damping motion
Nakano K; Chiba D; Ohshima N; Kasai S; Sato T; Nakatani Y; Sekiguchi K; Kobayashi K; Ono T
The Physical Society of Japan, 2012, Meeting Abstracts of the Physical Society of Japan, 67, 0, 531-531, Japanese, 1342-8349, 110009566772, AA11439205 - 19aCC-12 Detection of magnetization rotation in domain wall induced by spin transfer torque in Co/Ni nanowire III
Hiramatsu R; Koyama T; Chiba D; Fukami S; Ishiwata N; Nakatani Y; Ono T
The Physical Society of Japan, 2012, Meeting Abstracts of the Physical Society of Japan, 67, 0, 414-414, Japanese, 1342-8349, 110009599977, AA11439205 - 25pHF-7 Vortex resonance and rectifying effect
Goto M.; Hata H.; Yamaguchi A.; Nozaki Y.; Nakatani Y.; Yamaoka T.
The Physical Society of Japan (JPS), 03 Mar. 2011, Meeting abstracts of the Physical Society of Japan, 66, 1, 477-477, Japanese, 1342-8349, 110008713948, AA11439205 - 25pHF-8 Real-time detection of the vortex core resonance motion.
Nakano K; Chiba D; Ohshima N; Kasai S; Sato T; Nakatani Y; Sekiguchi K; Kobayashi K; Ono T
The Physical Society of Japan, 2011, Meeting Abstracts of the Physical Society of Japan, 66, 0, 478-478, Japanese, 1342-8349, 110008713949, AA11439205 - 26aPS-35 Temperature dependence of current-induced domain wall (DW) motion in Co/Ni nano-wires II
Ueda K; Ono T; Koyama T; Chiba D; Tanigawa H; Fukami S; Suzuki T; Ohshima N; Ishiwata N; Nakatani Y
The Physical Society of Japan, 2011, Meeting Abstracts of the Physical Society of Japan, 66, 0, 492-492, Japanese, 1342-8349, 110008714006, AA11439205 - 28aHF-8 Domain Wall Oscillator 2
Kondou K; Nakatani Y; Hiramatsu R; Chiba D; Fukami S; Ishiwata N; Ono T
The Physical Society of Japan, 2011, Meeting Abstracts of the Physical Society of Japan, 66, 0, 515-515, Japanese, 1342-8349, 110008714098, AA11439205 - 21aPS-31 Detection of magnetization precession in domain wall induced by the spin transfer torque in Co/Ni nanowire
Hiramatsu R; Kondou K; Koyama T; Chiba D; Fukami S; Ishiwata N; Nakatani Y; Ono T
The Physical Society of Japan, 2011, Meeting Abstracts of the Physical Society of Japan, 66, 0, 379-379, Japanese, 1342-8349, 110008758630, AA11439205 - 23aRA-7 Realization of Vortex Core Memory Cell
Nakano K; Chiba D; Ohshima N; Kasai S; Sato T; Nakatani Y; Sekiguchi K; Kobayashi K; Ono T
The Physical Society of Japan, 2011, Meeting Abstracts of the Physical Society of Japan, 66, 0, 441-441, Japanese, 1342-8349, 110008758864, AA11439205 - 23pRA-4 Temperature dependence of current-induced domain wall motion in perpendicularly magnetized Co/Ni nanowires
Ueda K; Ono T; Koyama T; Chiba D; Fukami S; Tanigawa H; Suzuki T; Oshima N; Ishiwata N; Nakatani Y
The Physical Society of Japan, 2011, Meeting Abstracts of the Physical Society of Japan, 66, 0, 450-450, Japanese, 1342-8349, 110008758898, AA11439205 - 23pRA-5 Effect of external magnetic field on threshold current density for current-induced domain wall displacement II
Koyama T; Ono T; Ueda K; Chiba D; Fukami S; Tanigawa H; Suzuki T; Ohshima N; Ishiwata N; Nakatani Y
The Physical Society of Japan, 2011, Meeting Abstracts of the Physical Society of Japan, 66, 0, 450-450, Japanese, 1342-8349, 110008758899, AA11439205 - Current-induced domain wall motion in Co/Ni nano-wires with different Co and Ni thicknesses
K. Ueda; D. Chiba; T. Koyama; G. Yamada; H. Tanigawa; S. Fukami; T. Suzuki; N. Ohshima; N. Ishiwata; Y. Nakatani; T. Ono
The authors have investigated magnetic domain wall motion induced by electric currents in ferromagnetic nano-wires made of Co/Ni multilayers. The thicknesses of Co and Ni layers were changed, whereas the numbers of layer stacks of Co and Ni were the same in all samples. The sample with thinner total Co/Ni thickness showed the lower threshold current density for the domain wall motion as an overall trend, which is qualitatively in agreement with the expectation by the theory based on the adiabatic spin-transfer model. The lowest threshold current density was 2.9×10 11 A/m 2 obtained in the sample with the total Co/Ni thickness of 3.4 nm and the wire width of 110 nm. © Published under licence by IOP Publishing Ltd., 01 Jan. 2011, Journal of Physics: Conference Series, 266, 1, 1742-6588, 1742-6596, 79952025378 - 24aWP-2 Dependence of vortex resonant frequency on magnetic structure in Fe_<19>Ni_<81> ferromagnetic disk
Goto M.; Hata H.; Yamaguchi A.; Nozaki Y.; Nakatani Y.; Yamaoka T.
The Physical Society of Japan (JPS), 18 Aug. 2010, Meeting abstracts of the Physical Society of Japan, 65, 2, 376-376, Japanese, 1342-8349, 110008097873, AA11439205 - Non-linear Vortex Motion Induced by the Simultaneous Application of rf and dc Currents in a Micron-sized Fe19Ni81 Disk
A. Yamaguchi; K. Motoi; H. Miyajima; T. Sato; Y. Nakatani
The translational mode of a vortex confined in a soft magnetic Fe19Ni81 circular disk and an elliptically shaped dot causes an asymmetric response in the rectifying planar Hall voltage and dc voltage output spectra. The symmetry breaking of these spectra has been experimentally observed, and is controlled by the simultaneous application of radio-frequency current and direct current. We can qualitatively explain the asymmetry of the rectifying spectra by the nonlinear resonator model, with gyration within a large radius around the vortex equilibrium positions causing the asymmetry., IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2010, IEEE Transactions on Magnetics 11th Joint MMM-Intermag, 46, 6, 1994-1997, English, 0018-9464, 1941-0069, 80021054412, WOS:000278037800186 - 20aPS-28 Reduction of threshold current density for domain wall displacement by shape control of wire
Koyama T; Nakatani Y; Ono T; Ueda K; Yamada G; Chiba D; Tanigawa H; Fukami S; Suzuki T; Ohshima N; Ishiwata N
The Physical Society of Japan, 2010, Meeting Abstracts of the Physical Society of Japan, 65, 0, 455-455, Japanese, 1342-8349, 110007654927, AA11439205 - 20pGJ-3 Current-induced domain wall motion in Co/Ni nano-wires with different Co and Ni thickness
Ueda K; Nakatani Y; Ono T; Koyama T; Yamada G; Chiba D; Tanigawa H; Fukami S; Suzuki T; Ohshima N; Ishiwata N
The Physical Society of Japan, 2010, Meeting Abstracts of the Physical Society of Japan, 65, 0, 466-466, Japanese, 1342-8349, 110007655053, AA11439205 - 20pGJ-4 Current-induced motion of multi domain walls in a Co/Ni wire with perpendicular magnetic anisotropy II
Yamada G; Nakatani Y; Ono T; Koyama T; Ueda K; Chiba D; Tanigawa H; Fukami S; Suzuki T; Ohshima N; Ishiwata N
The Physical Society of Japan, 2010, Meeting Abstracts of the Physical Society of Japan, 65, 0, 466-466, Japanese, 1342-8349, 110007655054, AA11439205 - 20pGJ-8 Switching magnetic vortex core by using a resonance state
Nakano K; Chiba D; Ohshima N; Kasai S; Nakatani Y; Sekiguchi K; Kobayashi K; Ono T
The Physical Society of Japan, 2010, Meeting Abstracts of the Physical Society of Japan, 65, 0, 467-467, Japanese, 1342-8349, 110007655058, AA11439205 - 24aWP-4 Switching of the magnetic vortex core by nano-second field pulses : Elliptical dot
Yamada K; Kasai S; Nakatani Y; Sato T; Sekiguchi K; Chiba D; Kobayashi K; Ono T
The Physical Society of Japan, 2010, Meeting Abstracts of the Physical Society of Japan, 65, 0, 376-376, Japanese, 1342-8349, 110008097875, AA11439205 - 24aWP-5 Effect of external magnetic field on threshold current density for current-induced domain wall displacement
Koyama T; Ono T; Ueda K; Chiba D; Tanigawa H; Fukami S; Suzuki T; Ohshima N; Ishiwata N; Nakatani Y
The Physical Society of Japan, 2010, Meeting Abstracts of the Physical Society of Japan, 65, 0, 377-377, Japanese, 1342-8349, 110008097876, AA11439205 - 25aPS-34 Domain Wall Oscillator
Kondou K; Nakatani Y; Chiba D; Fukami S; Ishiwata N; Ono T
The Physical Society of Japan, 2010, Meeting Abstracts of the Physical Society of Japan, 65, 0, 406-406, Japanese, 1342-8349, 110008097979, AA11439205 - 25aPS-43 Temperature dependence of current-induced domain wall (DW) motion in Co/Ni nano-wires
Ueda K; Ono T; Koyama T; Chiba D; Tanigawa H; Fukami S; Suzuki T; Ohshima N; Ishiwata N; Nakatani Y
The Physical Society of Japan, 2010, Meeting Abstracts of the Physical Society of Japan, 65, 0, 408-408, Japanese, 1342-8349, 110008097988, AA11439205 - Micromagnetics Simulation IV : Chapter 4 The Thermal Effect
HAYASHI N.; UESAKA Y.; NAKATANI Y.; FUKUSHIMA H.
日本磁気学会, 01 Jan. 2009, Magnetics Japan, 4, 1, 43-51, Japanese, 1880-7208, 10024834704, AA1211610X - 27aTF-10 Real-time detection of the current induced vortex dynamics by using the TMR effect
Nakano K; Nakatani Y; Ohshima N; Kasai S; Kobayashi K; Ono T
The Physical Society of Japan, 2009, Meeting Abstracts of the Physical Society of Japan, 64, 0, 430-430, Japanese, 1342-8349, 110007371276, AA11439205 - 27pTF-1 Real-Time Detection of the Magnetic Domain Wall Dynamics
Kondou K; Tanigawa H; Kasai S; Ohshima N; Nakatani Y; Kobayashi K; Ono T
The Physical Society of Japan, 2009, Meeting Abstracts of the Physical Society of Japan, 64, 0, 450-450, Japanese, 1342-8349, 110007371349, AA11439205 - 27pTF-2 Current-driven domain wall motion in Co/Ni wires with perpendicular magnetic anisotropy
Koyama T; Ono T; Tanigawa H; Yamada G; Ohshima N; Fukami S; Ishiwata N; Chiba D; Kasai S; Nakatani Y
The Physical Society of Japan, 2009, Meeting Abstracts of the Physical Society of Japan, 64, 0, 451-451, Japanese, 1342-8349, 110007371350, AA11439205 - 28aPS-101 Switching of the magnetic vortex core by nano-second current pulses : Elliptical dot
Yamada K; Kasai S; Nakatani Y; Kobayashi K; Kohno H; Thiaville Andre; Ono T
The Physical Society of Japan, 2009, Meeting Abstracts of the Physical Society of Japan, 64, 0, 480-480, Japanese, 1342-8349, 110007371469, AA11439205 - 28aPS-108 Current-induced domain wall motion in Co/Ni wires with perpendicular magnetic anisotropy
Tanigawa H; Ono T; Koyama T; Yamada G; Chiba D; Kasai S; Ohshima N; Fukami S; Ishiwata N; Nakatani Y
The Physical Society of Japan, 2009, Meeting Abstracts of the Physical Society of Japan, 64, 0, 482-482, Japanese, 1342-8349, 110007371476, AA11439205 - 28aPS-112 Injection of a single domain wall into a Co/Ni wire with perpendicular magnetic anisotropy
Yamada G; Ono T; Koyama T; Tanigawa H; Ohshima N; Fukami S; Ishiwata N; Chiba D; Kasai S; Nakatani Y
The Physical Society of Japan, 2009, Meeting Abstracts of the Physical Society of Japan, 64, 0, 483-483, Japanese, 1342-8349, 110007371479, AA11439205 - 25pPSA-27 Magnetic anisotropy constant of perpendicularly magnetized Co/Ni nano-wires
Ueda K; Nakatani Y; Ono T; Koyama T; Yamada G; Chiba D; Tanigawa H; Fukami S; Suzuki T; Ohshima N; Ishiwata N
The Physical Society of Japan, 2009, Meeting Abstracts of the Physical Society of Japan, 64, 0, 344-344, Japanese, 1342-8349, 110007497222, AA11439205 - 25pPSA-29 Current-induced motion of multi domain walls in a Co/Ni wire with perpendicular magnetic anisotropy
Yamada G; Nakatani Y; Ono T; Koyama T; Ueda K; Tanigawa H; Fukami S; Suzuki T; Ohshima N; Ishiwata N; Chiba D
The Physical Society of Japan, 2009, Meeting Abstracts of the Physical Society of Japan, 64, 0, 344-344, Japanese, 1342-8349, 110007497224, AA11439205 - 27aRA-4 Domain Wall Motion in High Magnetic Field
Kondou K; Nakatani Y; Ohshima N; Kasai S; Chiba D; Kobayashi K; Ono T
The Physical Society of Japan, 2009, Meeting Abstracts of the Physical Society of Japan, 64, 0, 369-369, Japanese, 1342-8349, 110007497318, AA11439205 - 27aRA-5 Current-induced domain wall motion in Co/Ni wire in magnetic field
Koyama T; Nakatani Y; Ono T; Yamada G; Ueda K; Tanigawa H; Fukami S; Suzuki T; Ohshima N; Ishiwata N; Chiba D
The Physical Society of Japan, 2009, Meeting Abstracts of the Physical Society of Japan, 64, 0, 369-369, Japanese, 1342-8349, 110007497319, AA11439205 - 27aRA-8 Real-time detection of the current induced vortex dynamics by using an MTJ
Nakano K; Kasai S; Nakatani Y; Ohshima N; Sekiguchi K; Chiba D; Kobayashi K; Ono T
The Physical Society of Japan, 2009, Meeting Abstracts of the Physical Society of Japan, 64, 0, 370-370, Japanese, 1342-8349, 110007497322, AA11439205 - Micromagnetics Simulation III : Chapter 3 Numerical Solution to Landau-Lifshitz-Gilbert Equation
HAYASHI N.; UESAKA Y.; NAKATANI Y.; FUKUSHIMA H.
日本磁気学会, 01 Oct. 2008, Magnetics Japan, 3, 10, 481-488, Japanese, 1880-7208, 10024327237, AA1211610X - Micromagnetics Simulation II : Chapter 2 Finite-Difference Method
HAYASHI N.; UESAKA Y.; NAKATANI Y.; FUKUSHIMA H.
日本磁気学会, 01 Jul. 2008, Magnetics Japan, 3, 7, 334-341, Japanese, 1880-7208, 10021155430, AA1211610X - Micromagnetics Simulation I : Chapter 1 Analytic Solution
HAYASHI N.; UESAKA Y.; NAKATANI Y.; FUKUSHIMA H.
日本磁気学会, 01 Apr. 2008, Magnetics Japan, 3, 4, 193-199, Japanese, 1880-7208, 10021154980, AA1211610X - 24aWL-12 Nucleation and Dynamics of Magnetic Vortices under Spin Current
Nakatani Y.; Shibata J.; Tatara G.; Kohno H.; Thiaville A.; Miltat J.
The Physical Society of Japan (JPS), 29 Feb. 2008, Meeting abstracts of the Physical Society of Japan, 63, 1, 476-476, Japanese, 1342-8349, 110007192049, AA11439205 - 21pQG-6 Stochastic pinning of domain wall driven by an external magnetic field
Tanigawa H; Koyama T; Bartkowiak Maciej; Nakatani Y; Kasai S; Ono T
The Physical Society of Japan, 2008, Meeting Abstracts of the Physical Society of Japan, 63, 0, 379-379, Japanese, 1342-8349, 110006983862, AA11439205 - 21pQG-9 Switching of the magnetic vortex core by nano-second current pulses II
Yamada K; Kasai S; Nakatani Y; Kobayashi K; Kohno H; Thiaville Andre; Ono T
The Physical Society of Japan, 2008, Meeting Abstracts of the Physical Society of Japan, 63, 0, 380-380, Japanese, 1342-8349, 110006983865, AA11439205 - 21pQG-14 Real-time detection of the current induced vortex dynamics by using the TMR effect
Nakano K; Nakatani Y; Ohshima N; Kasai S; Kobayashi K; Ono T
The Physical Society of Japan, 2008, Meeting Abstracts of the Physical Society of Japan, 63, 0, 381-381, Japanese, 1342-8349, 110006983870, AA11439205 - 24aWL-11 Real-time and real space imaging of the magnetic vortex resonant motion in a ferromagnetic circular disk
Kasai S; Fischer Peter; Im Mi-Young; Yamada K; Nakatani Y; Oshima K; Kobayashi K; Kohno H; Ono T
The Physical Society of Japan, 2008, Meeting Abstracts of the Physical Society of Japan, 63, 0, 476-476, Japanese, 1342-8349, 110007192048, AA11439205 - 23aPS-29 Real-time detection of the current induced vortex dynamics by using the TMR effect
Nakano K; Nakatani Y; Oshima N; Kasai S; Kobayashi K; Ono T
The Physical Society of Japan, 2008, Meeting Abstracts of the Physical Society of Japan, 63, 0, 431-431, Japanese, 1342-8349, 110007195859, AA11439205 - 23aPS-28 Switching of the magnetic vortex core by nano-second current pulses II
Yamada K; Kasai S; Nakatani Y; Kobayashi K; Kohno H; Thiaville Andre; Ono T
The Physical Society of Japan, 2008, Meeting Abstracts of the Physical Society of Japan, 63, 0, 431-431, Japanese, 1342-8349, 110007195860, AA11439205 - 24aWL-8 単一磁壁ダイナミクスの実時間観測(24aWL 微小領域磁性,領域3(磁性,磁気共鳴))
近藤 浩太; 谷川 博信; 葛西 伸哉; 大嶋 則和; 仲谷 栄伸; 小林 研介; 小野 輝男
一般社団法人 日本物理学会, 2008, 日本物理学会講演概要集, 63, 0, 475-475, Japanese, 1342-8349, 110007195982, AA11439205 - Computer Simulation of Spin Polarized Current Induced Magnetic Domain Wall Motion
NAKATANI Y.
日本応用磁気学会, 01 Jun. 2007, Magnetics Japan, 2, 6, 291-299, Japanese, 1880-7208, 10019927969, AA1211610X - 18pZC-9 Electrical switching of vortex core in a magnetic disk
Yamada K; Kasai S; Nakatan Y; Kobayashi K; Kohno H; Thiaville Andre; Ono T
The Physical Society of Japan, 2007, Meeting Abstracts of the Physical Society of Japan, 62, 0, 444-444, Japanese, 1342-8349, 110007140420, AA11439205 - 18pZC-1 Rectifying effect in magnetic nanowires
Yamaeuchi A; Miyajima H; Ono T; Suzuki Y; Nakatani Y; Yuasa S
The Physical Society of Japan, 2007, Meeting Abstracts of the Physical Society of Japan, 62, 0, 442-442, Japanese, 1342-8349, 110007140428, AA11439205 - 22pWB-1 Switching of the magnetic vortex core by nano-second current pulses
Yamada K; Kasai S; Nakatani Y; Kobayashi K; Kohno H; Thiaville Andre; Ono T
The Physical Society of Japan, 2007, Meeting Abstracts of the Physical Society of Japan, 62, 0, 486-486, Japanese, 1342-8349, 110007141412, AA11439205 - 29pSC-4 Threshold Current of Domain Wall Motion under Extrinsic Pinning, β-Term and Non-Adiabaticity
Tatara Gen; Takayama Toshihiko; Kohno Hiroshi; Shibata Junya; Nakatani Yoshinobu; Fukuyama Hidetoshi
The Physical Society of Japan (JPS), 04 Mar. 2006, Meeting abstracts of the Physical Society of Japan, 61, 1, 490-490, Japanese, 1342-8349, 110007180896, AA11439205 - Computer simulation of magnetization instability by spin-polarized current injection
NAKATANI Yoshinobu
30 Jan. 2006, 日本応用磁気学会研究会資料, 145, 23-29, Japanese, 1340-7562, 10017264893, AN00351217 - Domain-wall dynamics in nanowires and nanostrips
Andre Thiaville; Yoshinobu Nakatani
In nanowires or nanostrips, the magnetic domain walls have structures that depend sensitively on the transverse sizes of these samples. These domain-wall structures govern the dynamics of the walls under an applied field, so that rather different wall velocities can result from small changes in the sample transverse dimensions. These phenomena are first presented and discussed using results of micromagnetic simulations. In order to understand them, a model - valid in the limit of vanishing transverse dimensions - is introduced. It is shown that, however, this model applies also to the more complex domain-wall structures that exist at larger transverse sizes, qualitatively but even quantitatively in some cases. A procedure for determining the effective parameters of this model is given. Comparison to available experimental results is performed whenever possible., SPRINGER-VERLAG BERLIN, 2006, SPIN DYNAMICS IN CONFINED MAGNETIC STRUCTURES III, 101, 161-205, English, Book review, 0303-4216, WOS:000241944100005 - 23pXH-4 Magnetization reversal process in a ferromagnetic circular dot under current-induced resonant excitation
Kasai S; Yamada K; Nakatani Y; Kobayashi K; Kohno H; Ono T
The Physical Society of Japan, 2006, Meeting Abstracts of the Physical Society of Japan, 61, 0, 345-345, Japanese, 1342-8349, 110007178873, AA11439205 - 23aPS-29 Current-induced resonance by magnetic vortex : Current intensity dependence
Yamada K; Kasai S; Nakatani Y; Kobayashi K; Kohno H; Ono T
The Physical Society of Japan, 2006, Meeting Abstracts of the Physical Society of Japan, 61, 0, 320-320, Japanese, 1342-8349, 110007183032, AA11439205 - 19pYB-7 Dynamics of a magnetic vortex due to spin current
Shibata J.; Tatara G.; Kohno H.; Nakatani Y.; Otani Y.
The Physical Society of Japan (JPS), 19 Aug. 2005, Meeting abstracts of the Physical Society of Japan, 60, 2, 289-289, Japanese, 1342-8349, 110004538575, AA11439205 - 27aYP-7 Computer simulatoin of magnetic domain wall motion by spin polarized current injection
Nakatani Yoshinobu
The Physical Society of Japan (JPS), 04 Mar. 2005, Meeting abstracts of the Physical Society of Japan, 60, 1, 482-482, Japanese, 1342-8349, 110004535956, AA11439205 - Effect of the quadratic uniaxial anistropy term on the R/W properties of the perpendicular recording media
NAKATANI Yoshinobu; HAYASHI Nobuo; UESAKA Yasutaro; FUKUSHIMA Hiroshi
映像情報メディア学会, 10 Feb. 2005, ITE technical report, 29, 12, 11-16, Japanese, 1342-6893, 10015517027, AN1059086X - Effect of the quadratic uniaxial anistropy term on the R/W properties of the perpendicular recording media
NAKATANI Yoshinobu; HAYASHI Nobuo; UESAKA Yasutaro; FUKUSHIMA Hiroshi
The method which utilizes the quadratic uniaxial anistropy term to improve the thermal stability in the recording media was proposed. In this method, the thermal stability can be improved without increasing the write field. But it was predicted that the write field increases as K_2 term is increased when the easy axis of the magnetic moment and the write field is not parallel. In this paper, the effect of the quadratic uniaxial anistropy term on the write field was investigated by computer simulation. The results show that the read/write properties change by the effect of the term because the angle is large, therfore it is found that the write field was changed by the term., The Institute of Electronics, Information and Communication Engineers, 10 Feb. 2005, IEICE technical report. Magnetic recording, 104, 652, 11-16, Japanese, 0913-5685, 110003205543, AN10013050 - 電流による磁壁移動
多々良源; 河野浩; 柴田絢也; 仲谷栄伸; 山口明啓; 小野輝男
2005, 応用物理学会誌,74,1598-1602 (2005). 応用物理学学会, 74, 1598 - The magnetization reversal simulation of a perpendicular magnetization film
NISHIMURA K.; ENDO H.; UESAKA Y.; NAKATANI Y.; HAYASHI N.; FUKUSHIMA H.
21 Sep. 2004, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 28, 474-474, Japanese, 10013769918, AN10269644 - Magnetization Reversal of Single-Domain Particles Studied by Numerically Solving the Fokker-Planck Equation
FUKUSHIMA H.; UESAKA Y.; NAKATANI Y.; HAYASHI N.
The magnetization reversal of single-domain particles at finite temperatures is investigated by numerically solving the Fokker-Planck equation. The equation has singularity at two particular positions. For an axially symmetric system, the problem is surmounted by introducing a novel probability function. For a non-axially symmetric system, it is overcome by using the Cartesian coordinates at these points. The methods above are validated by calculating frequency prefactors and comparing them with those from approximate analytic formulas. For the axially symmetric system, the dependence of the switching time on parameters such as the applied field, the temperature, and the volume is expressed as an experimental formula. For the non-axially symmetric case, assuming that the oblique angle of an applied field to the easy axis is a few degrees, the solution is expanded in a truncated Fourier series. The dependence of the switching time on the applied field and the damping constant is calculated. The effect of a gyromagnetic term in the equation on the switching time is also studied., 日本応用磁気学会, 01 Sep. 2004, Journal of Magnetics Society of Japan, 28, 9, 957-962, Japanese, 0285-0192, 110002809830, AN0031390X - Measurement method of magnetic anisotropy energy constant 2
HIROSE K.; ENDO H.; UESAKA Y.; NAKATANI Y.; HAYASHI N.; FUKUSHIMA H.
01 Sep. 2003, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 27, 217-217, Japanese, 1340-8100, 10015761496, AN10269644 - Measurement of easy axis distribution
SANGUU T.; ENDO H.; UESAKA Y.; NAKATANI Y.; HAYASHI N.; FUKUSHIMA H.
01 Sep. 2003, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 27, 216-216, Japanese, 1340-8100, 10015761493, AN10269644 - Computer simulation of switching time of perpendicular film
YOSHINO M.; ENDO H.; UESAKA Y.; NAKATANI Y.; HAYASHI N.; FUKUSHIMA H.
01 Sep. 2003, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 27, 98-98, Japanese, 1340-8100, 10015761181, AN10269644 - Compuater simulation of domain wall motion with Bloch point in nano wire
NAKATANI Y.; HAYASHI N.
01 Sep. 2002, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 26, 99-99, Japanese, 1340-8100, 10015759915, AN10269644 - Effect of magnetization on read/write properties of AFC media
NAKATANI Y.; HAYASHI N.; UESAKA Y.; FUKUSHIMA H.
01 Sep. 2002, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 26, 175-175, Japanese, 1340-8100, 10015760147, AN10269644 - Micromagnetic Study of Magnetization Configuration on Single Pole Type Head
MOCHIZUKI M.; ISHIKAWA C.; IDE H.; NAKAMOTO K.; NAKATANI Y.; HAYASHI N.
01 Sep. 2002, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 26, 438-438, Japanese, 1340-8100, 10015760837, AN10269644 - Thermal stability of AFC recording media
NAKATANI Yoshinobu
07 Mar. 2002, 日本応用磁気学会研究会資料, 124, 17-24, Japanese, 1340-7562, 10007792786, AN00351217 - Computer simulation of switching time of magnetic particle
TAKAHASI T.; FUJIWARA T.; ENDO H.; UESAKA Y.; NAKATANI Y.; HAYASHI N.; FUKUSHIMA H.
01 Sep. 2001, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 25, 142-142, Japanese, 1340-8100, 10007796786, AN10269644 - Measurement of anisotropy field and easy axis distribution
TOMIZAWA H.; ENDO H.; UESAKA Y.; NAKATANI Y.; HAYASHI N.; FUKUSHIMA H.
01 Sep. 2001, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 25, 141-141, Japanese, 1340-8100, 10007796784, AN10269644 - Effect of thermal fluctuation of AFC recording media
NAKATANI Y.; HAYASHI N.; UESAKA Y.; FUKUSHIMA H.
01 Sep. 2001, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 25, 406-406, Japanese, 1340-8100, 10007797506, AN10269644 - Read/write properties of AFC recording media
NAKATANI Y.; HAYASHI N.; UESAKA Y.; FUKUSHIMA H.
01 Sep. 2001, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 25, 405-405, Japanese, 1340-8100, 10007797503, AN10269644 - Compuater simulation model for AFC recording media
NAKATANI Y.; HAYASHI N.; UESAKA Y.; FUKUSHIMA H.
01 Sep. 2001, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 25, 404-404, Japanese, 1340-8100, 10007797501, AN10269644 - Exchange interaction of single layer perpendicular media and R/W properties
UESAKA Y.; ENDO H.; NAKATANI H. Y.; HAYASHI N.; FUKUSHIMA H.
01 Sep. 2001, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 25, 403-403, Japanese, 1340-8100, 10007797499, AN10269644 - Galvanomagnetic effect of permalloy nano-ring wire II magnetization properties
Niiyama T.; Kasai S.; Hirota Y.; Miyajima H.; Nakatani Y.; Hayashi N.
The Physical Society of Japan (JPS), 09 Mar. 2001, Meeting abstracts of the Physical Society of Japan, 56, 1, 415-415, Japanese, 1342-8349, 110002157400, AA11439205 - Computer simulation of magnetization switching of particles with groves
ENDO H.; UESAKA Y.; NAKATANI Y.; HAYASHI N.; FUKUSHIMA H.
01 Sep. 2000, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 24, 104-104, Japanese, 1340-8100, 10007795266, AN10269644 - Influence of particle size and Ku distribution and exchange on thermal stability
AKAGI F.; YOSHIDA K.; NAKATANI Y.; HAYASHI N.
01 Sep. 2000, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 24, 393-393, Japanese, 1340-8100, 10007796103, AN10269644 - Computer simulation of switching field and time of single magnetic particle
ABE R.; ENDO H.; UESAKA Y.; NAKATANI Y.; HAYASHI N.; FUKUSHIMA H.
01 Sep. 2000, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 24, 398-398, Japanese, 1340-8100, 10007796117, AN10269644 - Numerical Solution of LLG Equation by Backward-difference Method
KADOGAKI N.; KAWABATA Y.; NAKATANI Y.; HAYASHI N.
01 Sep. 2000, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 24, 389-389, Japanese, 1340-8100, 10007796092, AN10269644 - Acceleration of LaBonte's Iteration by Multigrid Method
KAWABATA Y.; HIRANO S.; HAYASHI N.; NAKATANI Y.
01 Sep. 2000, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 24, 390-390, Japanese, 1340-8100, 10007796094, AN10269644 - MAMMOS Copy Simulation : Effect of Temperature Distribution
NAKATANI Y.; HAYASHI N.; IMAI S.; AWANO H.; OHTA N.
01 Sep. 2000, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 24, 438-438, Japanese, 1340-8100, 10007796231, AN10269644 - Magnetization Distribution in Displacement Layer on DWDD
NAKATANI Y.; KOBAYASHI T.; SHIRATORI T.
01 Sep. 2000, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 24, 443-443, Japanese, 1340-8100, 10007796247, AN10269644 - Computer Simulation of Magnetic Domain Wall Motion in a Magnetic Strip Line
NAKATANI Y; HAYASHI N; ONO T; MIYAJIMA H
01 Sep. 2000, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 24, 197-197, Japanese, 1340-8100, 10007795573, AN10269644 - Velocity of Magnetic Domain Wall Motion in a Magnetic Strip Line
NAKATANI Y; HAYASHI N; ONO T; MIYAJIMA H
01 Sep. 2000, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 24, 198-198, Japanese, 1340-8100, 10007795576, AN10269644 - Switching field of a fine magnetic particle with surface anisotropy
NAKATANI Y.; HAYASHI N.; UESAKA Y.; KITAKAMI O.; SHIMADA
07 Feb. 2000, 電気学会研究会資料. MAG, マグネティックス研究会, 2000, 1, 37-41, Japanese, 10019056580, AN00346760 - Computer simulation of R/W properties of longitudinal medea
UESAKA Y.; NAKATANI Y.; HAYASHI N.; FUKUSHIMA H.
01 Oct. 1999, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 23, 438-438, Japanese, 10005326275, AN10269644 - Computer Simulation of Wall motion by Wall Energy
NAKATANI Y.; KAMATA K.; KOBAYASHI T.; SHIRATORI T.
01 Oct. 1999, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 23, 84-84, Japanese, 10005325313, AN10269644 - Computer simulation of magnetization switching of particles with various shapes
ENDO H.; UESAKA Y.; NAKATANI Y.; HAYASHI N.
01 Oct. 1999, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 23, 135-135, Japanese, 10005325429, AN10269644 - Grain arrangement model in magnetic recording simulation
OSHIMA T.; NAKAYANI Y.; HAYASHI N.
01 Oct. 1999, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 23, 458-458, Japanese, 10005326330, AN10269644 - Numerical Solution of LLG Equation Based on Basic Relaxation Method
KAWABATA Y.; HIRANO S.; HAYASHI Y.; NAKATANI Y.
01 Oct. 1999, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 23, 454-454, Japanese, 10005326317, AN10269644 - Computer Simulation of frequency factor of fine magnetic particle
NAKATANI Y.; HAYASHI N.; UESAKA Y.; FUKUSHIMA H.
01 Oct. 1999, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 23, 452-452, Japanese, 10005326309, AN10269644 - Numerical Solution of LLG Equation by Multigrid Method
HIRANO S.; KAWABATA Y.; HAYASHI N.; NAKATANI Y.
01 Oct. 1999, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 23, 455-455, Japanese, 10005326321, AN10269644 - Influences of α on recording characteristics at high frequencies
AKAGI F.; IGARASHI M.; YOSHIDA K.; NAKATANI Y.; HAYASHI N.
01 Sep. 1998, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 22, 330-330, Japanese, 10002824750, AN10269644 - Effect of Surface Anistropy on Seitching Field of Magnetic Fine Particle
NAKATANI Y.; HAYASHI N.; UESAKA Y.; FUKUSHIMA H.; KITAKAMI O.; SHIMADA Y.
01 Sep. 1998, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 22, 384-384, Japanese, 10002824887, AN10269644 - Anisotropy energy constant of longitudinal media measured by 45 degree method
UESAKA Y.; NAKATANI Y.; HAYASHI N.; FUKUSHIMA H.; INABA N.
01 Sep. 1998, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 22, 471-471, Japanese, 10002825113, AN10269644 - MAMMOS Copy Somulation for Circular Domain
NAKATANI Y.; HAYASHI N.; AWANO H.; OHTA N.
01 Sep. 1998, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 22, 497-497, Japanese, 10002825197, AN10269644 - MAMMOS COpy Simulation for Crescent Shaped Domain
NAKATANI Y.; HAYASHI N.; AWANO H.; OHTA N.
01 Sep. 1998, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 22, 498-498, Japanese, 10002825200, AN10269644 - MAMMOS Copy Simulation(One-Dimensional Case)
GUNJI S.; OSHIMA T.; KAMATA K.; NAKATANI Y.; HAYASHI N.
01 Sep. 1998, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 22, 499-499, Japanese, 10002825204, AN10269644 - MAMMOS Copy Simulation by Laser
KAMATA K.; OSHIMA T.; GUNJI S.; NAKATANI Y.; HAYASHI N.
01 Sep. 1998, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 22, 500-500, Japanese, 10002825208, AN10269644 - Simulation of Thermal Fluctuation of Magnetic Recording Media
UESAKA Y.; NAKATANI Y.; HAYASHI N.; FUKUSHIMA H.
Thermal fluctuation of the magnetization and recorded pattern in longitudinal and perpendicular recording media was investigated by using the Monte Carlo simulation method. Distribution of the grain size in a medium increases the effect of thermal fluctuation of the magnetization and recorded pattern. Perpendicular recording is superior to longitudinal recording from the thermal fluctuation point of view. In longitudinal recording after three years decay, it is difficult to obtain a higher recording density than 10 Gb/in^2 at 423 kFCl. In perpendicular recording, the recording density of 50 Gb/in^2 is possible to be obtained., 日本応用磁気学会, 01 Jul. 1998, Journal of Magnetics Society of Japan, 22, 7, 1111-1118, Japanese, 0285-0192, 110002810110, AN0031390X - Computer Simulation of Effect of Thermal Fluctuation on Magnetic Recording Media
NAKATANI Y.; HAYASHI N.; UESAKA Y.; FUKUSHIMA H.
29 Jan. 1998, 日本応用磁気学会研究会資料, 103, 13-19, Japanese, 1340-7562, 10002521165, AN00351217 - Effefct of grain shape in magnetic recording media simulation
NAKATANI Yoshinobu; HAYASHI Nobuo; UESAKA Yasutaro; FUKUSHIMA Hiroshi
01 Oct. 1997, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 21, 260-260, Japanese, 10002730510, AN10269644 - Solving LLG equation for low-dissipation media
KAWASHIMA Y.; HAYASHI N.; NAKATANI Y.
01 Oct. 1997, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 21, 269-269, Japanese, 10002730533, AN10269644 - Influence of hard magnet film stractures on read characteristics of MR heads.
ISHIKAWA C.; TOTUSUKA K.; IGARASHI M.; SUZUKI Y.; NAKATANI Y.; HAYASHI N.
01 Oct. 1997, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 21, 414-414, Japanese, 10002730899, AN10269644 - Monte Carlo Simulation of Thermal Fluctuation in Longitudinal and Perpendicular Recording Media
UESAKA Yasutaro; TAKAHASHI Yoshio; NAKATANI Yoshinobu; HAYASHI Nobuo; FUKUSHIMA Hiroshi
Thermal fluctuation in magnetization of longitudinal and perpendicular recording media was calculated using a Monte Carlo simulation method. Distribution of grain size in a medium increases the effect of thermal fluctuation in magnetization. Perpendicular recording is superior to longitudinal recording from thermal fluctuation point of view. In longitudinal recording, the effect of thermal fluctuation increases with increasing recording density, but in perpendicular recording the effect decreases with increasing recording density., The Institute of Image Information and Television Engineers, 21 Nov. 1996, ITEJ Technical Report, 20, 61, 7-13, Japanese, 0386-4227, 110003680572, AN00352231 - Monte Carlo simulation of recording media
UESAKA Yasutaro; NAKATANI Yoshinobu; HAYASHI Nobuo; FUKUSHIMA Hiroshi
01 Sep. 1996, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 20, 16-16, Japanese, 10002728782, AN10269644 - Read/write properties of perpendicular recording media by thermal fluctuation
NAKATANI Yoshinobu; HAYASHI Nobuo; UESAKA Yasutaro; FUKUSHIMA Hiroshi
01 Sep. 1996, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 20, 18-18, Japanese, 10002728787, AN10269644 - Read/write properties of longitudinal recording media by thermal fluctuation
NAKATANI Yoshinobu; HAYASHI Nobuo; UESAKA Yasutaro; FUKUSHIMA Hiroshi
01 Sep. 1996, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 20, 17-17, Japanese, 10002728784, AN10269644 - Monte Carlo Simulation of Thermal Fluctuation Aftereffect
UESAKA Y.; NAKATANI Y.; HAYASHI N.; FUKUSHIMA H.
01 Sep. 1995, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 19, 405-405, Japanese, 10002646982, AN10269644 - Computer Simulation of Thermal Fractuation After Effect using Langeving Equation
NAKATANI Yoshinobu; HAYASHI Nobuo; UESAKA Yasutaro
01 Sep. 1995, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 19, 406-406, Japanese, 10002646986, AN10269644 - Analysis of output and magnetization configuration of shielded MR head
FUJIMOTO K.; TOTSUKA K.; UESAKA Y.; SAITOH I.; FUKUI H.; YOSHIHARA I.; NAKATANI Y.; HAYASHI N.
01 Sep. 1995, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 19, 224-224, Japanese, 10002646503, AN10269644 - Dependence of output characteristics on casy direction in MR head. -Simulation-
ISHIKAWA C.; FUJIMOTO K.; UESAKA Y.; NAKATANI Y.; HAYASHI N.
01 Sep. 1995, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 19, 220-220, Japanese, 10002646493, AN10269644 - Computer Simulation of Output and Magnetization configuration of MR Sensor Dependence of MR response to a cycle of transverse external field on direction of easy magnetization of SAL
FUJIMOTO Kazuhisa; TOTSUKA Kaori; UESAKA Yasutaro; FUKUI Hiroshi; NAKATANI Yoshinobu; HAYASHI Nobuo
In an exchange biased magneto-resistive (MR) sensor with a soft adjacent layer (SAL), a MR response to a cycle of a transverse external field has a hysteresis due to a vortex nucleated at a corner of the sensing area of the SAL. To prevent the nucleation of the vortex, the dependence of the MR response on the direction of the easy magnetization of the SAL has been investigated using a computer simulation. It has been found that the MR response has no hysteresis if the direction of the easy magnetization of the SAL tilts 30 to 60 degrees from the longitudinal direction of the sensor to the direction of the magnetization of the SAL in the biased state., The Institute of Electronics, Information and Communication Engineers, 19 May 1995, IEICE technical report. Magnetic recording, 95, 49, 1-8, Japanese, 110003186179, AN10013050 - Numerical simulation of magnetization reversal using super - computer
Uesaka Yasutaro; Fujimoto Kazuhisa; Yoshihara Ikuo; Nakatani Yoshinobu; Hayashi Nobuo
Magnetic structure and magnetization reversal mechaism of magneto-resistive head were analysed by using super-computer. Magnetic films were divided into rectangular cells and each magnetic moment was assumed to precess according to the Landau-Lifshitz-Gilbert equation. For the demagnetizing field calculation, which is the most time cosuming process, Fast Fourier Transform was used. Then, the computation time became less than 1/20 than the time for the direct calculation method. The effect of uniform applied field on output was calculated and small peaks due to magnetization reversals of SAL (Soft Adjacent Layer) were observed., Information Processing Society of Japan (IPSJ), 27 Oct. 1994, IPSJ SIG Notes, 1994, 92, 9-16, Japanese, 110002932150, AN10463942 - Computer simulation of thin-film media noise
Yoshida Kazuetsu; Uesaka Yasutaro; Hara Miki; Nakatani Yoshinobu; Hayashi Nobuo
Computer simulation using the autocorreelation function along the track direction was used to investigate the relationship between thin-film media noise and both the orientation of easy axis and the exchange interaction.Preferentially orienting the easy axis in the circumferential direction decreases the media noise and increases the strength of output signal.On the other hand,exchange interaction slightly increases media noise and reduces the signal-to-noise ratio.Preferential orientation of the easy axis,however,improves the signal-to-noise ratio more effectively than does preventing intergranular exchange interaction., The Institute of Electronics, Information and Communication Engineers, 19 May 1993, IEICE technical report. Magnetic recording, 93, 29, 29-35, Japanese, 110003186284, AN10013050 - 8)Dynamical Calculation of Magnetization Reversal in Small Particles
上坂 保太郎; 仲谷 栄伸; 林 信夫
The Institute of Image Information and Television Engineers, 20 Nov. 1992, The Journal of the Institute of Television Engineers of Japan, 46, 11, 1526-1526, Japanese, 0386-6831, 110003675411, AN00151466
Lectures, oral presentations, etc.
- Simulation of spin-orbit-torque switching of a perpendicular nanomagnet assited byy DMI
J. Watanabe; K. Yamada; Y. Nakatani
Intermag2023, Peer-reviewed
May 2023 - Logic operations of magnetic-skyrmion chirality via a branched nanowire
Y. Nakatani; K. Yamada; A. Hirohata
Intermag2023, Peer-reviewed
May 2023 - Current-niduced magnetic octupole domain-wall dynamics
M. Wu; T. Chen; T. Nomoto; H. Isshiki; Y. Nakatani; T. Higo; T.Tomita; K. Kondou; R. Arita; S. Nakatsuji; Y. Otani
Oral presentation, MMM2022, Peer-reviewed
Oct. 2022 - Thermal Agitation of Magnetization Dynamics Induced by Electric-field
S. Kanai; Y. Nakatani; F. Matsukura; H. Ohno
JEMS2022, Peer-reviewed
26 Jun. 2022 - Thermal Effect in Electric-field Induced Magnetization Dynamics in a Nanoscale Magnetic Tunnel Junction
S. Kanai; Y. Nakatani; F. Matsukura; H. Ohno
ICMFS2022, Peer-reviewed
13 Jun. 2022 - Multiple-valued Memory Utilized Chiral Magnetic Skyrmion
J. Watanabe; K. Yamada; and; Y. Nakatani
ICMFS2022, Peer-reviewed
12 Jun. 2022 - Controlling antiferromagnetic skyrmion motions in an angelfish racetrack by electric field
K. Hamada; K. Nishi; K. Yamada; Y. Nakatani
ICMFS2022, Peer-reviewed
12 Jun. 2022 - Simulation of the switching probability in nanomagnets with perpendicular anisotropy",
K. Kawakami; K. Yamada; Y. Nakatani
ICMFS2022, Peer-reviewed
12 Jun. 2022 - Electrical discrimination of magnetic-skyrmion chirality via spin-orbit and-transfer torques in a branched nanowire
K. Yamada; A. Hirohata; Y. Nakatani
2022 Joint MMM-Intermag Conference, Peer-reviewed
Jan. 2022 - Determination of the Dzyaloshinskii-Moriya interaction from a single magnetic domain image using machine learning
K. Tanabe; S. Hasegawa; M. Hayashi; M. Kawaguchi; T. Sawa; K. Yamada; Y. Nakatani
2021 Intermag Conference, Peer-reviewed
Apr. 2021 - Discrimination of skyrmion chirality via spin-orbit and -transfer torques for logic operation
K. Yamada; A. Hirohata; Y. Nakatani
IOP institute of Physics, CRIM 2021: Magnetic Skyrmions,, Peer-reviewed
2021 - Computer simulation of domain wall motion induced by a slope electric field.
S. Murayama; K. Yamada; Y. Nakatani
English, 2015 IEEE MAGNETICS CONFERENCE (INTERMAG), IEEE
2015
2015 2015 - 9pBF-7 Domain wall dynamics in the presence of the Dzyaloshinskii-Moriya interaction
Yoshimura Yoko; Kim Kab-Jin; Taniguchi Takuya; Ueda Kohei; Hiramatsu Ryo; Moriyama Takahiro; Tanigawa Hironobu; Suzuki Tetsuhiro; Kariyada Eiji; Nakatani Yoshinobu; Ono Teruo
Japanese, Meeting abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS)
22 Aug. 2014
22 Aug. 2014- 22 Aug. 2014 - 9pBF-5 Switching of a Magnetic Vortex Core in a Pac-man Disk using a Single Current Pulse
Yamada Keisuke; Sato Tomonori; Nakatani Yoshinobu
Japanese, Meeting abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS)
22 Aug. 2014
22 Aug. 2014- 22 Aug. 2014 - 28aAF-4 Switching of the Magnetic Vortex Core in a Pac-man Disk
Yamada Keisuke; Sato Tomonori; Nakatani Yoshinobu
Japanese, Meeting abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS)
05 Mar. 2014
05 Mar. 2014- 05 Mar. 2014 - 28aAF-3 Observation of metastable bound state between domain walls in an asymmetric Co/Ni nanowire II
Hiramatsu R.; Kim Kab-Jin; Hata H.; Taniguchi T.; Tanigawa H.; Kariyada H.; Suzuki T.; Nakatani Y.; Moriyama T.; Ono T.
Japanese, Meeting abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS)
05 Mar. 2014
05 Mar. 2014- 05 Mar. 2014 - Influence of spin Hall effect for current-induced domain wall motion in a perpendicularly magnetized Co/Ni nanowire
Yoshimura Y.; Koyama T.; Moriyama T.; Kim Kab-Jin; Chiba D.; Nakatani Y.; Fukami S.; Yamanouchi M.; Ohno H.; Ono T.
Japanese, Meeting abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS)
26 Aug. 2013
26 Aug. 2013- 26 Aug. 2013 - Switching of the Magnetic Vortex Core in Elliptical Disks by Nano-second Field Pulses
Yamada Keisuke; Sato Tomonori; Nakatani Yoshinobu; Kasai Shinya; Chiba Daichi; Kobayashi Kensuke; Thiaville Andre; Ono Teruo
Japanese, Meeting abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS)
26 Aug. 2013
26 Aug. 2013- 26 Aug. 2013 - Mechanism change of current-induced magnetic domain wall motion in multilayered Co/Ni nanowires
Ueda K.; Kim K-J.; Hiramatsu R.; Moriyama T.; Chiba D.; Tanigawa H.; Kariyada E.; Suzuki T.; Nakatani Y.; Ono T.
Japanese, Meeting abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS)
26 Aug. 2013
26 Aug. 2013- 26 Aug. 2013 - 26aPS-18 Detection of magnetization rotation in domain wall induced by spin transfer torque in Co/Ni nanowire
Kim Kab-Jin
Japanese, Meeting abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS)
26 Mar. 2013
26 Mar. 2013- 26 Mar. 2013 - 27pXA-6 Current pulse width dependence of magnetic domain wall motion in the presence of bias magnetic field
Kim Kab-Jin; Chiba D.; Nakatani Y.; Fukami S.; Yamanouchi M.; Ohno H.; Ono T.
English, Meeting abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS)
26 Mar. 2013
26 Mar. 2013- 26 Mar. 2013 - 27pXA-5 Temperature Dependence of Current-Induced Magnetic Domain Wall Motion in a Multilayered Co/Ni Nanowire with MgO Cap
上田 浩平; 小野 輝男; 平松 亮; キムカブジン; 森山 貴広; 千葉 大地; 谷川 博信; 苅屋田 英嗣; 鈴木 哲広; 仲谷 栄伸
Japanese, Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan, http://ci.nii.ac.jp/naid/110009644376
2013
2013 2013 - 26aPS-17 Current-induced domain wall motion in a perpendicularly magnetized Co/Ni nanowire under in-plane magnetic field (III)
Yoshimura Y; Koyama T; Moriyama T; Chiba D; Tanigawa H; Kariyada E; Suzuki T; Nakatani Y; Ono T
Japanese, Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan, http://ci.nii.ac.jp/naid/110009644236
2013
2013 2013 - 27aAA-3 Manipulation of the vortex core damping motion
Nakano K; Chiba D; Ohshima N; Kasai S; Sato T; Nakatani Y; Sekiguchi K; Kobayashi K; Ono T
Japanese, Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan, http://ci.nii.ac.jp/naid/110009566772
2012
2012 2012 - 24aPS-29 Additivity of magnetic domain wall velocities induced by current and field
Koyama T; Ueda K; Chiba D; Fukami S; Ishiwata N; Kohno H; Nakatani Y; Kobayashi K; Ono T
Japanese, Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan, http://ci.nii.ac.jp/naid/110009566583
2012
2012 2012 - 24aPS-28 Detection of magnetization rotation in domain wall induced by spin transfer torque
Hiramatsu R; Kondou K; Koyama T; Chiba D; Fukami S; Ishiwata N; Nakatani Y; Ono T
Japanese, Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan, http://ci.nii.ac.jp/naid/110009566582
2012
2012 2012 - 27aAA-8 Temperature Dependence of Spin Polarization of Current in Co/Ni Nanowire Estimated from Current-Induced Magnetic Domain Wall Motion
Ueda K; Nakatani Y; Ono T; Koyama T; Hiramatsu R; Chiba D; Fukami S; Tanigawa H; Suzuki T; Ohshima N; Ishiwata N
Japanese, Meeting Abstracts of the Physical Society of Japan, 一般社団法人 日本物理学会, http://ci.nii.ac.jp/naid/110009566777
2012
2012 2012 - 20aCC-10 Current-induced domain wall motion in a perpendicularly magnetized Co/Ni nanowire under in-plane magnetic field (II)
Yoshimura Y; Koyama T; Chiba D; Fukami S; Yamanouchi M; Ohno H; Nakatani Y; Ono T
Japanese, Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan, http://ci.nii.ac.jp/naid/110009600017
2012
2012 2012 - 27aAA-10 High-field motion of magnetic domain wall in (Co/Ni) nanostrips
Yamada K; Jamet Jean-Pierre; Nakatani Y; Ueda K; Mougin Alexandra; Thiaville Andre; Ono T; Ferre Jacques
Japanese, Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan, http://ci.nii.ac.jp/naid/110009566779
2012
2012 2012 - 27aAA-9 Current-induced domain wall motion in a perpendicularly magnetized Co/Ni nanowire under in-plane magnetic field
Yoshimura Y; Koyama T; Chiba D; Fukami S; Yamanouchi M; Ohno H; Nakatani Y; Ono T
Japanese, Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan, http://ci.nii.ac.jp/naid/110009566778
2012
2012 2012 - Influence of hard magnet film stractures on read characteristics of MR heads.
ISHIKAWA C.; TOTUSUKA K.; IGARASHI M.; SUZUKI Y.; NAKATANI Y.; HAYASHI N.
Japanese, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan
01 Oct. 1997
01 Oct. 1997- 01 Oct. 1997 - Solving LLG equation for low-dissipation media
KAWASHIMA Y.; HAYASHI N.; NAKATANI Y.
Japanese, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan
01 Oct. 1997
01 Oct. 1997- 01 Oct. 1997 - Monte Carlo Simulation of Thermal Fluctuation in Longitudinal and Perpendicular Recording Media
UESAKA Yasutaro; TAKAHASHI Yoshio; NAKATANI Yoshinobu; HAYASHI Nobuo; FUKUSHIMA Hiroshi
Japanese, ITEJ Technical Report, The Institute of Image Information and Television Engineers, Thermal fluctuation in magnetization of longitudinal and perpendicular recording media was calculated using a Monte Carlo simulation method. Distribution of grain size in a medium increases the effect of thermal fluctuation in magnetization. Perpendicular recording is superior to longitudinal recording from thermal fluctuation point of view. In longitudinal recording, the effect of thermal fluctuation increases with increasing recording density, but in perpendicular recording the effect decreases with increasing recording density.
21 Nov. 1996
21 Nov. 1996- 21 Nov. 1996 - Read/write properties of longitudinal recording media by thermal fluctuation
NAKATANI Yoshinobu; HAYASHI Nobuo; UESAKA Yasutaro; FUKUSHIMA Hiroshi
Japanese, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan
01 Sep. 1996
01 Sep. 1996- 01 Sep. 1996 - Read/write properties of perpendicular recording media by thermal fluctuation
NAKATANI Yoshinobu; HAYASHI Nobuo; UESAKA Yasutaro; FUKUSHIMA Hiroshi
Japanese, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan
01 Sep. 1996
01 Sep. 1996- 01 Sep. 1996 - Monte Carlo simulation of recording media
UESAKA Yasutaro; NAKATANI Yoshinobu; HAYASHI Nobuo; FUKUSHIMA Hiroshi
Japanese, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan
01 Sep. 1996
01 Sep. 1996- 01 Sep. 1996 - Dependence of output characteristics on casy direction in MR head. -Simulation-
ISHIKAWA C.; FUJIMOTO K.; UESAKA Y.; NAKATANI Y.; HAYASHI N.
Japanese, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan
01 Sep. 1995
01 Sep. 1995- 01 Sep. 1995 - Analysis of output and magnetization configuration of shielded MR head
FUJIMOTO K.; TOTSUKA K.; UESAKA Y.; SAITOH I.; FUKUI H.; YOSHIHARA I.; NAKATANI Y.; HAYASHI N.
Japanese, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan
01 Sep. 1995
01 Sep. 1995- 01 Sep. 1995 - Computer Simulation of Thermal Fractuation After Effect using Langeving Equation
NAKATANI Yoshinobu; HAYASHI Nobuo; UESAKA Yasutaro
Japanese, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan
01 Sep. 1995
01 Sep. 1995- 01 Sep. 1995 - Monte Carlo Simulation of Thermal Fluctuation Aftereffect
UESAKA Y.; NAKATANI Y.; HAYASHI N.; FUKUSHIMA H.
Japanese, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan
01 Sep. 1995
01 Sep. 1995- 01 Sep. 1995 - Computer Simulation of Output and Magnetization configuration of MR Sensor Dependence of MR response to a cycle of transverse external field on direction of easy magnetization of SAL
FUJIMOTO Kazuhisa; TOTSUKA Kaori; UESAKA Yasutaro; FUKUI Hiroshi; NAKATANI Yoshinobu; HAYASHI Nobuo
Japanese, IEICE technical report. Magnetic recording, The Institute of Electronics, Information and Communication Engineers, In an exchange biased magneto-resistive (MR) sensor with a soft adjacent layer (SAL), a MR response to a cycle of a transverse external field has a hysteresis due to a vortex nucleated at a corner of the sensing area of the SAL. To prevent the nucleation of the vortex, the dependence of the MR response on the direction of the easy magnetization of the SAL has been investigated using a computer simulation. It has been found that the MR response has no hysteresis if the direction of the easy magnetization of the SAL tilts 30 to 60 degrees from the longitudinal direction of the sensor to the direction of the magnetization of the SAL in the biased state.
19 May 1995
19 May 1995- 19 May 1995 - Numerical simulation of magnetization reversal using super - computer
Uesaka Yasutaro; Fujimoto Kazuhisa; Yoshihara Ikuo; Nakatani Yoshinobu; Hayashi Nobuo
Japanese, IPSJ SIG Notes, Information Processing Society of Japan (IPSJ), http://id.nii.ac.jp/1001/00029888/, Magnetic structure and magnetization reversal mechaism of magneto-resistive head were analysed by using super-computer. Magnetic films were divided into rectangular cells and each magnetic moment was assumed to precess according to the Landau-Lifshitz-Gilbert equation. For the demagnetizing field calculation, which is the most time cosuming process, Fast Fourier Transform was used. Then, the computation time became less than 1/20 than the time for the direct calculation method. The effect of uniform applied field on output was calculated and small peaks due to magnetization reversals of SAL (Soft Adjacent Layer) were observed.
27 Oct. 1994
27 Oct. 1994- 27 Oct. 1994 - Computer simulation of thin-film media noise
Yoshida Kazuetsu; Uesaka Yasutaro; Hara Miki; Nakatani Yoshinobu; Hayashi Nobuo
Japanese, IEICE technical report. Magnetic recording, The Institute of Electronics, Information and Communication Engineers, Computer simulation using the autocorreelation function along the track direction was used to investigate the relationship between thin-film media noise and both the orientation of easy axis and the exchange interaction.Preferentially orienting the easy axis in the circumferential direction decreases the media noise and increases the strength of output signal.On the other hand,exchange interaction slightly increases media noise and reduces the signal-to-noise ratio.Preferential orientation of the easy axis,however,improves the signal-to-noise ratio more effectively than does preventing intergranular exchange interaction.
19 May 1993
19 May 1993- 19 May 1993 - 8)Dynamical Calculation of Magnetization Reversal in Small Particles
上坂 保太郎; 仲谷 栄伸; 林 信夫
Japanese, The Journal of the Institute of Television Engineers of Japan, The Institute of Image Information and Television Engineers
20 Nov. 1992
20 Nov. 1992- 20 Nov. 1992
Research Themes
- 磁気スキルミオンのカイラリティを利用したメモリ・ロジックデバイスの開発
仲谷 栄伸
日本学術振興会, 科学研究費助成事業 基盤研究(C), 電気通信大学, 基盤研究(C), 23K04526
01 Apr. 2023 - 31 Mar. 2026 - Determination of the magnetic parameter using pattern recognition and machine learning
Yoshinobu Nakatani
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B), The University of Electro-Communications, Grant-in-Aid for Scientific Research (B), We show that machine learning can be used to extract material parameters from a single image obtained in experiments. The DzyaloshinskMoriya (DM) interaction and the magnetic anisotropy distribution of thin-film heterostructures, parameters that are critical in developing next-generation storage class magnetic memory technologies, are estimated from a magnetic domain image. Micromagnetic simulation is used to generate thousands of random images for training and model validation. A convolutional neural network system is employed as the learning tool. The DM exchange constant of typical Co-based thin-film heterostructures is studied using the trained system: the estimated values are in good agreement with experiments. Moreover, we show that the system can independently determine the magnetic anisotropy distribution, demonstrating the potential of pattern recognition. This approach can considerably simplify experimental processes and broaden the scope of materials research., 19H02553
01 Apr. 2019 - 31 Mar. 2022 - Spin-orbitronics and device application
ONO Teruo; KOHNO hiroshi; NAKATANI yoshinobu; NAGAHAMA taro; NAKAMURA kohji; HAYASHI masamitsu; CHIBA daichi; TANIYAMA tomoyasu
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Specially Promoted Research, Kyoto University, Grant-in-Aid for Specially Promoted Research, This project established the field of Spin-orbitronics by exploiting the spin-orbit interaction of electrons in solids to form new materials with novel functionalities and find new physics. New approach for designing strong magnetic anisotropy materials, novel way for efficient magnetization control, and new method for controlling spins in antiferromagnets were developed, which will enable development of high speed, energy efficient electronic devices and technological innovations., 15H05702
2015 - 2019 - Studies of the observation of magnetic skyrmions in ferromagnetic thin films
KEISUKE Yamada; NAKATANI Yoshinobu; ONO Teruo; YAMAGUCHI Akinobu; TANABE Kenji
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Gifu University, Grant-in-Aid for Challenging Exploratory Research, The observation of Skyrmion at room temperature were investigated using ferromagnetic thin films with perpendicular magnetic anisotropy. (1) In the experimental research using Co/Ni multilayer films, it observed the movement of the magnetic domain structures in magnetic wires, however it did not observed the Skyrmions. (2) In the research using numerical simulations, we investigated the nucleation and annihilation conditions of Skyrmions in Co / Ni multilayers and clarified the conditions that the Skyrmion exists stably at room temperature. As other research, we investigated that (3) the magnitude of the topological Hall effect depending on the magnetization structure in the cross-shaped magnetic wire, and that (4) the changing the magnetic domain structures in the Ni wire on the piezoelectric substrate LiNbO3., 15K13272
01 Apr. 2015 - 31 Mar. 2018 - Simulation analysys of the domain wall motion by spin current
Nakatani Yoshinobu
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C), The University of Electro-Communications, Grant-in-Aid for Scientific Research (C), Recently a storage system, which uses a magnetic domain wall as an information carrier was proposed, and the domain wall have been studied intensively. Because the domain wall motion velocity is related to the operation speed of the storage system, it is required to obtain the conditions for fast domain wall motion, and to investigate the domain wall motion mechanism. In this research, the effect of the Dzyaroshinskii-Moriya interaction on the domain wall motion induced by a spin current, a magnetic field, and an electric field were investigated by computer simulation, and obtained the conditions for fast domain wall motion, and revealed the domain wall motion mechanism., 26390008
01 Apr. 2014 - 31 Mar. 2017 - Development of Novel Spin Dynamics Devices
Ono Teruo; MORIYAMA Takahiro; KIM KabJin; CHIBA Daich; KOHNO Hiroshi; NAKATANI Yoshinobu
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (S), Kyoto University, Grant-in-Aid for Scientific Research (S), The purpose of this project is to develop novel spin devices that utilize the current-induced spin dynamics in non-uniform spin structure, such as a magnetic domain wall and a magnetic vortex. We succeeded in demonstrating the operation of the spin devices such as domain wall memory and vortex core memory. Furthermore, we obtained unexpected results such as the observation of spin motive force in gyrating vortex core and the modulation of ferromagnetic transition temperature of Cobalt by electric field gating., 23221008
31 May 2011 - 31 Mar. 2016 - Control of spin currents and functions
TANAKA Masaaki; SUZUKI Yoshishige; SHIMIZU Hiromasa; NAKATANI Yoshinobu
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Priority Areas, The University of Tokyo, Grant-in-Aid for Scientific Research on Priority Areas, This research members are the leaders of each group in A05 "Functions and Control of Spin Currents". We explored principles of control and transformations of various signals and their functions, and proposed new devices and realized their operations. Cooperating with other groups, we studied spin-polarized-current-controlled devices, spin current, microwave and thermal devices, optical spintronics devices, spin-current-induced magnetization reversal devices, and theories and designs. Furthermore, we enhanced exchange of ideas and collaborations. We organized the 6th International Conference on Physics and Applications of Spin Related Phenomena in Semiconductors (PASPS-VI)) in Tokyo, August 2010 (Conference chair : Masaaki Tanaka), and contributed the worldwide advance of this field., 19048019
2007 - 2010 - Computer simulation of magnetic vortex core switching by spin current
NAKATANI Yoshinobu
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Priority Areas, The University of Electro-Communications, Grant-in-Aid for Scientific Research on Priority Areas, Recently, there are many works relating to the vortex core dynamics by spin current. In this research the mechanism of the vortex core rotation and switching by spin current are investigated by using computer simulation. We also investigate the conditions to use this mechanism for magnetic devices. Because these simulation requires huge amount of the computation time, we propose the method to accelerate the calculation speed by using the graphic processing unit., 19048021
2007 - 2010 - ブロッホライン対書き込み操作のシミュレーション
仲谷 栄伸
日本学術振興会, 科学研究費助成事業 奨励研究(A), 電気通信大学, 奨励研究(A), 磁性薄膜中に存在する磁壁上の磁化構造であるブロッホラインを情報の記憶単位として用いるブロッホライン記憶装置は、次世代の不揮発性高密度個体記憶装置として現在研究が進められている。情報の書き込み操作であるブロッホライン対の書き込みの操作の一つとして、ブロッホポイント注入法が提案されている。この手法ではまずunwindingな二つのブロッホライン対を生成し、それぞれの内側のブロッホラインを消去することで、windingで安定なブロッホライン対を生成する。内側のブロッホラインの消去過程において、ブロッホポイントの発生が仮定されているが、実験ではブロッホポイントは直接観測することは出来ない。ここでは計算機シミュレーションを行なうことで、ブロッホライン書き込み操作の一部であるブロッホポイントの注入によるブロッホライン対の消滅過程の詳細を求めた。これらの計算は東京大学大型計算機センターのスーパーコンピュータを用いて行なった。計算は三次元の動的計算であるために、その結果として膨大な数値データが得られるが、これを詳細に解析するためには数値の視覚化が必要になる。この作業は研究室のワークステーション上で行なった。数値データと視覚化した画像データは膨大な量になるために、専用のハードディスク装置を購入した。, 05750285
1993 - 1994