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Satoshi Okamoto

Section

Institute of Multidisciplinary Research for Advanced Materials

Job title

Professor

Degree

博士（工学）（東北大学）
修士（工学）（東北大学）

researchmap

https://researchmap.jp/read0052234

J-GLOBAL ID

200901086910904388

e-Rad No.

10292278

ORCID

https://orcid.org/0000-0002-1302-7769

Professional Memberships 3

電気学会
日本金属学会
日本応用磁気学会

Research Interests 2

thin film
magnetic material

Research Areas 1

Nanotechnology/Materials / Crystal engineering / Magnetic Thin Films

Papers 247

Ultra-low core loss and high core saturation magnetization of nanocrystalline Fe-B-P-Cu powder cores fabricated by using a hot-press process Peer-reviewed

Masato Kuno, Nobuhisa Ono, Yosuke Imano, Akiri Urata, Hidehiko Oikawa, Satoshi Okamoto

Acta Materialia　294　121159-121159　2025/08
Publisher: Elsevier BV
DOI： 10.1016/j.actamat.2025.121159 　

ISSN： 1359-6454
Feature Analysis on Iron Loss Behaviors of Various Soft Magnetic Cores under DC Bias Fields Peer-reviewed

T. Onuma, N. Ono, S. Okamoto

Journal of the Magnetics Society of Japan　49　(1)　21-26　2025/01/01
Publisher: The Magnetics Society of Japan
DOI： 10.3379/msjmag.2501r005 　

ISSN： 1882-2924

eISSN： 1882-2932
Feature extraction and classification of microstructure and magnetic tomography images of an advanced Nd-Fe-B sintered magnet Peer-reviewed

Tomomi Suwa, Keisuke Ishigami, Motohiro Suzuki, Satoshi Okamoto

Japanese Journal of Applied Physics　63　(11)　117002-117002　2024/11/01
Publisher: IOP Publishing
DOI： 10.35848/1347-4065/ad8995 　

ISSN： 0021-4922

eISSN： 1347-4065

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Abstract Although the microstructure and magnetic tomography images of an advanced Nd-Fe-B sintered magnet were previously reported [Takeuchi (2022)], the relationship between these three-dimensional images has not been well analyzed. In this work, a feature extraction method of the histogram of oriented gradients and a classification method of uniform manifold approximation and projection are employed for this issue. The microstructural features, with the information of magnetic domain structures superimposed, are classified into two groups depending on the external magnetic fields, resulting in the successful classification of distinct microstructural features corresponding to different magnetization states. These differences in the microstructural features are difficult to detect by human recognition. Further detailed analysis of these microstructural features may clarify the key microstructures for the nucleation of reversed domains and their propagations.
Clustering First-order reversal curve diagram using the Gaussian mixture model and the Davies Bouldin index Peer-reviewed

Ruixuan Ying, Takuya Taniguchi, Koki Nabeta, Keisuke Ishigami, Nobuaki Kikuchi, Satoshi Okamoto

Japanese Journal of Applied Physics　2024/10/21
Publisher: IOP Publishing
DOI： 10.35848/1347-4065/ad892d 　

ISSN： 0021-4922

eISSN： 1347-4065

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Abstract In our energy-consuming society, understanding magnetization reversal in permanent magnets is crucial for improving energy conversion efficiency between electric energy and mechanical energy. First-order reversal curves (FORCs) have enabled qualitative studies of reversal mechanisms, however, further understanding based on quantitative analysis is still difficult due to the complexity of FORC diagrams. We introduce a machine-learning based approach combining the Gaussian mixture model and the Davies-Bouldin index to separate characteristic features in FORC diagrams of Nd-Fe-B magnets. The clustering method is evaluated using several FORC diagrams obtained at different temperatures, and we also demonstrated hysteresis loop reconstruction using the clustered FORC diagrams.
Effect of Compaction Pressure on Core Loss in Fe–Ni Powder Cores for High-Frequency Applications Peer-reviewed

Mai Phuong Nguyen, Shigeyoshi Yoshida, Satoshi Okamoto, Takamichi Miyazaki, Yasushi Endo

IEEE Transactions on Magnetics　60　(9)　1-4　2024/09
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
DOI： 10.1109/tmag.2024.3402273 　

ISSN： 0018-9464

eISSN： 1941-0069
Multimodal iron loss analyses based on magnetization processes for various soft magnetic toroidal cores Peer-reviewed

Nobuhisa Ono, Yuji Uehara, Tomoyuki Onuma, Takuya Taniguchi, Nobuaki Kikuchi, Satoshi Okamoto

Journal of Magnetism and Magnetic Materials　603　172222-172222　2024/08
Publisher: Elsevier BV
DOI： 10.1016/j.jmmm.2024.172222 　

ISSN： 0304-8853
Direct observation of current-induced nonlinear spin torque in Pt-Py bilayers Peer-reviewed

Toshiyuki Kodama, Nobuaki Kikuchi, Takahiro Chiba, Satoshi Okamoto, Seigo Ohno, Satoshi Tomita

Physical Review B　109　(21)　2024/06/13
Publisher: American Physical Society (APS)
DOI： 10.1103/physrevb.109.214419 　

ISSN： 2469-9950

eISSN： 2469-9969
Thermal Stability of Magnetization States and Reversal Fields from the Perspective of Landau Theory Peer-reviewed

Mitsumata C., Kotsug M., Okamoto S.

Transaction of the Magnetics Society of Japan Special Issues　8　(1)　21-24　2024/05/01
Publisher: The Magnetics Society of Japan
DOI： 10.20819/msjtmsj.24tr811 　

eISSN： 2432-0471

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A method for achieving both the thermal stability of magnetic signals and the reduction of the magnetization reversal field was investigated using the Landau theory. We give some examples of slope shapes in a free-energy landscape, and performs calculations for reversal fields. It is clarified that linear slopes without irregularities are suitable for the energy landscape to reduce the switching field. We also show that the method of suppressing the reduction in the energy barrier height and reducing the reversal magnetic field by bonding the soft phase/hard phase contributes to flattening the energy landscape. It is shown that the energy distribution of the domain wall motion studied in a previous simulation is consistent with the linear energy landscape in Landau theory.
Fe-based amorphous powder cores with low core loss and improvement of permeability Peer-reviewed

Mai Phuong Nguyen, Shigeyoshi Yoshida, Satoshi Okamoto, Takamichi Miyazaki, Yasushi Endo

AIP Advances　14　(2)　2024/02/01
Publisher: AIP Publishing
DOI： 10.1063/9.0000771 　

eISSN： 2158-3226

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Fe-based amorphous powder cores of Fe–Si–B–Cr–C magnetic powder and phenolic binder were fabricated, and the effects of annealing and compaction pressure on the soft magnetic properties and core loss were investigated. The formation of Fe–B and α-Fe (Si) phases was confirmed at the annealing temperature above 773 K. The density gradually increased from 5.3 to 5.5 g/cm3 as annealing temperature increased, resulting in the saturation magnetization 4πMs increased to 1.0 T at 773 K. The effect of compaction pressure was studied by using samples annealed at 723 K. Both the density and 4πMs enhanced with compaction pressure from 980 to 1960 MPa. The real part of permeability µ’ remained constant for the frequency up to 2 MHz. The initial value of µ’ increased from 25 to 38 with compaction pressure. Consequently, at Bm of 50 mT and frequency of 100 kHz, the considerably low core loss of 67 kW/m3 was obtained. The low core loss and moderately high permeability of Fe–Si–B–Cr–C amorphous powder core across a wide frequency range indicate its potential for application in high frequency electronic components.
Soft magnetic properties of Fe-Ni powder cores in the high frequency range International-journal Peer-reviewed

Mai Phuong Nguyen, Shigeyoshi Yoshida, Satoshi Okamoto, Sho Muroga, Takamichi Miyazaki, Yasushi Endo

AIP Advances　14　(1)　2024/01/01
Publisher: AIP Publishing
DOI： 10.1063/9.0000719 　

eISSN： 2158-3226

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Fe-Ni cores are excellent candidates for switching regulator inductors, transformers, reactors and in-line noise filters. Herein the influence of the phenol binder content on the microstructure and magnetic properties of Fe-50 wt% Ni powder cores in the high frequency range is investigated. Regardless of the binder content, all cores form a disordered A1 phase. The saturation magnetization (4πMs) and initial permeability increase as the binder content decreases. The core with a binder content of 0.5 wt% shows a relatively high 4πMs of 1.38 T and the highest permeability value of 70.9. Moreover, the total core loss (Pcv) with frequency ranges from 5 kHz to 1 MHz under a magnetic flux density of 10 mT depending on the binder content. A binder content of 3.0 wt% significantly reduces Pcv in the high frequency range above 100 kHz. At a frequency of 500 kHz, the Pcv values are 154.9, 128.7, and 133.8 kW/m3 for the cores with binder contents of 0.3, 0.5, and 1.0 wt%, respectively, but the value drastically decreases to 60.5 kW/m3 for a binder content of 3.0 wt%. Thus, the binder, which acts as an insulator layer between particles, affects the eddy current and consequently, Pcv. These results demonstrate that Fe-Ni powder cores exhibit excellent soft magnetic properties at various frequencies and suggest that a binder content of 3.0 wt% may realize optimal properties for future high frequency applications.
Analysis on bimodal complex permeability spectrum of a noise suppression sheet and single constituent flakes Peer-reviewed

Toshiyuki Igarashi, Shingo Tamaru, Nobuaki Kikuchi, Shigeyoshi Yoshida, Satoshi Okamoto

Journal of Magnetism and Magnetic Materials　590　171640-171640　2024/01
Publisher: Elsevier BV
DOI： 10.1016/j.jmmm.2023.171640 　

ISSN： 0304-8853
Core Loss Measurement of Metal Composite Materials for High Frequency using Resonant Method Peer-reviewed

Yuji Uehara, Kenji Kawano, Yuki Sato, Satoshi Okamoto

IEEJ Transactions on Fundamentals and Materials　143　(12)　374-378　2023/12/01
Publisher: Institute of Electrical Engineers of Japan (IEE Japan)
DOI： 10.1541/ieejfms.143.374 　

ISSN： 0385-4205

eISSN： 1347-5533
Feature Analysis on B–H Curves of Dust Cores Under the Application of DC Bias Field Peer-reviewed

Tomoyuki Onuma, Zhenzhuang Li, Satoshi Okamoto

IEEE Transactions on Magnetics　59　(11)　1-5　2023/11
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
DOI： 10.1109/tmag.2023.3281548 　

ISSN： 0018-9464

eISSN： 1941-0069
Accuracy Investigation of High-Frequency Core-Loss Measurement for Low-Permeability Magnetic Materials Peer-reviewed

Yuki Sato, Yuji Uehara, Satoshi Okamoto, Shigeyoshi Yoshida, Yasushi Endo, Nobuhisa Ono, Nobuto Misono, Hirokazu Matsumoto

IEEE Transactions on Magnetics　59　(11)　1-5　2023/11
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
DOI： 10.1109/tmag.2023.3283955 　

ISSN： 0018-9464

eISSN： 1941-0069
Analysis on Iron Loss of Sendust Dust Cores Based on Magnetization Reversal Processes Peer-reviewed

Nobuhisa Ono, Yuji Uehara, Yasushi Endo, Shigeyoshi Yoshida, Nobuaki Kikuchi, Hidehiko Oikawa, Satoshi Okamoto

IEEE Transactions on Magnetics　59　(11)　1-5　2023/11
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
DOI： 10.1109/tmag.2023.3287892 　

ISSN： 0018-9464

eISSN： 1941-0069
高特性永久磁石内部の磁気ヒステリシス曲線に沿った磁区変化挙動

宇根康裕, 竹内誠, 鈴木基寛, 小林慎太郎, 小谷佳範, 中村哲也, 菊池伸明, Anton BOLYACHKIN, Hossein SEPEHRI-AMIN, 大久保忠勝, 宝野和博, 岡本聡

電気製鋼　94　3-13　2023/06/16
Effect of film thickness on microwave assisted switching behavior

Nobuaki Kikuchi, Katsunari Sato, Masatoshi Hatayama, Takehito Shimatsu, Satoshi Okamoto

2023 IEEE International Magnetic Conference - Short Papers (INTERMAG Short Papers)　2023/05
Publisher: IEEE
DOI： 10.1109/intermagshortpapers58606.2023.10228446 　
Understanding the Coercivity of Ga-Containing Nd-Fe-B Sintered Magnets from Feature Extraction and Selection of X-Ray Diffraction Patterns via Dimension Reduction and Sparse Modeling

Keisuke Ishigami, Tomoyuki Onuma, Akira Kato, Masao Yano, Tetsuya Shoji, Tetsuya Nakamura, Satoshi Okamoto

2023 IEEE International Magnetic Conference (INTERMAG)　23820880　2023/05
Publisher: IEEE
DOI： 10.1109/intermag50591.2023.10265093 　
Recent Unrevealing on Magnetic Hysteresis of Permanent Magnets Invited Peer-reviewed

Satoshi Okamoto

Journal of the Japan Institute of Metals and Materials　87　(5)　150-157　2023/05/01
Publisher: Japan Institute of Metals
DOI： 10.2320/jinstmet.ja202201 　

ISSN： 0021-4876

eISSN： 1880-6880 2433-7501
Spin-Current-Driven Permeability Variation for Time-Varying Magnetic Metamaterials Peer-reviewed

Toshiyuki Kodama, Nobuaki Kikuchi, Satoshi Okamoto, Seigo Ohno, Satoshi Tomita

Physical Review Applied　19　(4)　2023/04/26
Publisher: American Physical Society (APS)
DOI： 10.1103/physrevapplied.19.044080 　

eISSN： 2331-7019
Microwave-assisted switching in granular media with continuous magnetic overlayers for interaction control Peer-reviewed

Nobuaki Kikuchi, Katsunari Sato, Takehito Shimatsu, Satoshi Okamoto

Japanese Journal of Applied Physics　62　(SB)　SB1015-SB1015　2023/03/01
Publisher: IOP Publishing
DOI： 10.35848/1347-4065/ac9910 　

ISSN： 0021-4922

eISSN： 1347-4065

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Abstract Optimizing switching behavior under a microwave field is a key issue for microwave-assisted magnetic recording. We study the effect of inter-grain exchange coupling induced by a continuous magnetic layer on microwave-assisted switching of CoCrPt-SiO₂ granular media. The microwave assistance effect is improved in the low-frequency region by introducing the inter-grain exchange coupling, but the coupling reduces the critical frequency. The maximum assistance effect is almost independent of the film structure since the dual effect cancels each other. Micromagnetic simulations also show similar results on exchange coupling between grains. These results indicate that the inter-grain exchange coupling can be used to optimize the critical frequency of the media in practical applications.
Thermal activation on microwave-assisted magnetization switching in Co/Pt nanodot arrays Peer-reviewed

Satoshi Mizutani, Nobuaki Kikuchi, Masatoshi Hatayama, Takehito Shimatsu, Satoshi Okamoto

Japanese Journal of Applied Physics　62　(SB)　SB1012-SB1012　2023/03/01
Publisher: IOP Publishing
DOI： 10.35848/1347-4065/ac9533 　

ISSN： 0021-4922

eISSN： 1347-4065

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Abstract The magnetization switching field is efficiently reduced by exciting precession with a microwave field of GHz frequency. Analytical calculations based on the Landau–Lifshitz–Gilbert equation have revealed that the effect of the thermal activation process plays an important role in magnetization switching behavior under a microwave field. In this study, we experimentally investigated the microwave-assisted magnetization switching (MAS) behavior of Co/Pt nanodot arrays under various microwave field conditions. Experimental results were compared with the calculated effective energy barrier height of MAS. Consequently, all the experimental MAS behaviors can be explained by the effect of thermal activation, but quantitative discussion will require accurate experimental studies.
Co-planar waveguide ferromagnetic resonance spectroscopy of cobalt/platinum superlattice metamaterials Peer-reviewed

Satoshi Tomita, Nobuaki Kikuchi, Satoshi Okamoto

Japanese Journal of Applied Physics　62　(SB)　SB1010-SB1010　2023/03/01

DOI： 10.35848/1347-4065/ac931a 　

ISSN： 0021-4922

eISSN： 1347-4065
Crystallographic and Magnetic Domains in Heat-Treated Fe–N Alloy Containing α″-Fe16N2 Phase Peer-reviewed

Takehiro Tamaoka, Satoshi Okamoto, Yasukazu Murakami

Shape Memory and Superelasticity　9　(2)　293-299　2023/02/08
Publisher: Springer Science and Business Media LLC
DOI： 10.1007/s40830-023-00417-1 　

ISSN： 2199-384X

eISSN： 2199-3858
Permeability Control of Ferromagnetic Wires for Time-varying Spintronic Metamaterials

Toshiyuki Kodama, Nobuaki Kikuchi, Satoshi Okamoto, Seigo Ohno, Satoshi Tomita

2023 IEEE International Magnetic Conference - Short Papers, INTERMAG Short Papers 2023 - Proceedings　2023

DOI： 10.1109/INTERMAGShortPapers58606.2023.10228637 　
Real picture of magnetic domain dynamics along the magnetic hysteresis curve inside an advanced permanent magnet Peer-reviewed

Makoto Takeuchi, Motohiro Suzuki, Shintaro Kobayashi, Yoshinori Kotani, Tetsuya Nakamura, Nobuaki Kikuchi, Anton Bolyachkin, Hossein Sepehri-Amin, Tadakatsu Ohkubo, Kazuhiro Hono, Yasuhiro Une, Satoshi Okamoto

NPG Asia Materials　14　(1)　2022/08/19
Publisher: Springer Science and Business Media LLC
DOI： 10.1038/s41427-022-00417-0 　

ISSN： 1884-4049

eISSN： 1884-4057

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Abstract In the long history of permanent magnet research for more than 100 years, three-dimensional magnetic microscopy has been eagerly awaited to elucidate the origin of the magnetic hysteresis of permanent magnets. In this study, we succeeded in observing the three-dimensional magnetic domain structure of an advanced high-coercivity Nd-Fe-B-based permanent magnet throughout the magnetic hysteresis curve using a recently developed hard X-ray magnetic tomography technique. Focused-ion-beam-based three-dimensional scanning electron microscopy was employed to study the relationship between the observed magnetic domains and the microstructure of the magnet for the same observing volume. Thermally demagnetized and coercivity states exhibit considerably different magnetic domain structures but show the same periodicity of 2.3 μm, indicating that the characteristic length of the magnetic domain is independent of the magnetization states. Further careful examination revealed some unexpected magnetic domain behaviors, such as running perpendicular to the magnetic easy axis and reversing back against the magnetic field. These findings demonstrate a wide variety of real magnetic domain behaviors along the magnetic hysteresis inside a permanent magnet.
Spintronic Materials and Their Properties Investigated by Synchrotron Radiation Invited Peer-reviewed

Teruo ONO, Satoshi OKAMOTO, Daichi CHIBA, Masaki MIZUGUCHI, Ko MIBU

Vacuum and Surface Science　65　(5)　218-223　2022/05/10
Publisher: Surface Science Society Japan
DOI： 10.1380/vss.65.218 　

ISSN： 2433-5835

eISSN： 2433-5843
Thermal activation in microwave-assisted magnetization switching and its effect on the switching behavior of granular media Peer-reviewed

Nobuaki Kikuchi, Katsunari Sato, Satoshi Okamoto, Osamu Kitakami, Takehito Shimatsu, Hirofumi Suto

Physical Review B　105　(5)　054430　2022/02/25
Publisher: American Physical Society (APS)
DOI： 10.1103/physrevb.105.054430 　

ISSN： 2469-9950

eISSN： 2469-9969
Temperature dependence of site-resolved Fe magnetic moments in ThMn12-type Sm(Fe1−Co )12 compounds studied via synchrotron Mössbauer spectroscopy Peer-reviewed

D. Ogawa, T. Fukazawa, S. Li, T. Ueno, S. Sakai, T. Mitsui, T. Miyake, S. Okamoto, S. Hirosawa, Y.K. Takahashi

Journal of Magnetism and Magnetic Materials　552　169188-169188　2022/02
Publisher: Elsevier BV
DOI： 10.1016/j.jmmm.2022.169188 　

ISSN： 0304-8853
Magnetic Domain Structure Observation for Initial Magnetization and Demagnetization Processes of a Nd-Fe-B Hot-Deformed Magnet Using Soft X-ray Magnetic Circular Dichroism Microscopy Peer-reviewed

M. Takeuchi, T. Yomogita, N. Kikuchi, K. Toyoki, S. Kobayashi, Y. Kotani, T. Nakamura, K. Hioki, S. Okamoto

Journal of the Japan Institute of Metals and Materials　86　(1)　1-7　2022/01/01
Publisher: Japan Institute of Metals
DOI： 10.2320/jinstmet.j2021041 　

ISSN： 0021-4876

eISSN： 1880-6880 2433-7501
Development of a high-sensitivity VNA-FMR spectrometer with field modulation detection and its application to magnetic characterization

Shingo Tamaru, Tatsuya Yamamoto, Tomoyuki Onuma, Nobuaki Kikuchi, Satoshi Okamoto

Electronics and Communications in Japan　104　(3)　2021/09/01
Publisher: John Wiley and Sons Inc
DOI： 10.1002/ecj.12320 　

ISSN： 1942-9541 1942-9533
Development of a High Sensitivity VNA-FMR Spectrometer with Field Modulation Detection and its Application to Magnetic Characterization Peer-reviewed

Shingo Tamaru, Tatsuya Yamamoto, Tomoyuki Onuma, Nobuaki Kikuchi, Satoshi Okamoto

IEEJ Transactions on Fundamentals and Materials　5　(5)　295-300　2021/05/01

DOI： 10.1541/ieejfms.141.295 　

ISSN： 0385-4205

eISSN： 1347-5533
Intrinsic hard magnetic properties of Sm(Fe,Co)12−xTix compound with ThMn12 structure Peer-reviewed

A. Makurenkova, D. Ogawa, P. Tozman, S. Okamoto, S. Nikitin, S. Hirosawa, K. Hono, Y.K. Takahashi

Journal of Alloys and Compounds　861　158477-158477　2021/04
Publisher: Elsevier BV
DOI： 10.1016/j.jallcom.2020.158477 　

ISSN： 0925-8388
Experimental approaches for micromagnetic coercivity analysis of advanced permanent magnet materials Invited Peer-reviewed

Satoshi Okamoto

Science and Technology of Advanced Materials　22　(1)　124-134　2021/02/12
Publisher: Informa UK Limited
DOI： 10.1080/14686996.2021.1874836 　

ISSN： 1468-6996

eISSN： 1878-5514
Time-resolved imaging of an operating hard-disk-drive write head using nano-beam x-ray magnetic circular dichroism Peer-reviewed

H. Suto, A. Kikitsu, Y. Kotani, T. Maeda, K. Toyoki, H. Osawa, N. Kikuchi, S. Okamoto, T. Nakamura

Journal of Applied Physics　128　133903-133903　2020/11
Direct detection and stochastic analysis on thermally activated domain-wall depinning events in micropatterned Nd-Fe-B hot-deformed magnets Peer-reviewed

T. Yomogita, S. Okamoto, N.. Kiikuchi, O. Kitakami, H. Sepehri-Amin, Y. K..Takahashi, T. Ohkubo, K. Hono, K. Hioki, A. Hattori

Acta Materialia　201　7-13　2020/09

DOI： 10.1016/j.actamat.2020.09.074 　

ISSN： 1359-6454
Coercivity Analysis and Magnetization Reversal Mechanism in Permanent Magnets Invited Peer-reviewed

S. Okamoto

Journal of Japanese Society of Powder Powder Metallurgy　67　666-674　2020/06
Magnetics and Optics Research FOREWORD

Satoshi Okamoto, Hiro Munekata, Taichi Goto, Makoto Kohda, Iwao Matsuda, Koji Sekiguchi, Yu Shiratsuchi, Roman Antos

JAPANESE JOURNAL OF APPLIED PHYSICS　59　2020/04

DOI： 10.35848/1347-4065/ab75dd 　

ISSN： 0021-4922

eISSN： 1347-4065
Magnetization manipulation induced by nonlocal spin injection from a perpendicular spin polarizer: nano-beam X-ray MCD study using an order-sorting-aperture collection method Peer-reviewed

Hirofumi Suto, Nobuaki Kikuchi, Satoshi Okamoto, Kentaro Toyoki, Yoshinori Kotani, Tetsuya Nakamura

Applied Physics Express　13　(4)　043002-043002　2020/04/01
Publisher: IOP Publishing
DOI： 10.35848/1882-0786/ab7bcb 　

ISSN： 1882-0778

eISSN： 1882-0786
Imaging of transient magnetization dynamics of Co/Pt multilayer dots with X-ray magnetic circular dichroism excited by microwaves Peer-reviewed

N. Kikuchi, T. Yomogita, K. Sato, S. Okamoto, O. Kitakami, H. Osawa, M. Suzuki, K. Toyoki, Y. Kotani, T. Nakamura

Japanese Journal of Applied Physics　59　(SE)　SEED03-SEED03　2020/04/01
Publisher: IOP Publishing
DOI： 10.35848/1347-4065/ab6cb1 　

ISSN： 0021-4922

eISSN： 1347-4065
Broadband and high-sensitivity permeability measurements on a single magnetic particle by transformer coupled permeameter Peer-reviewed

S. Tamaru, N. Kikuchi, T. Igarashi, S. Okamoto, H. Kubota, S. Yoshida

Journal of Magnetism and Magnetic Materials　501　166434-1-166434-7　2020/01
Temperature dependent magnetization reversal process of a Ga-doped Nd-Fe-B sintered magnet based on first-order reversal curve analysis Peer-reviewed

Satoshi Okamoto, Kazunori Miyazawa, Takahiro Yomogita, Nobuaki Kikuchi, Osamu Kitakami, Kentaro Toyoki, David Billington, Yoshinori Kotani, Tetsuya Nakamura, Taisuke Sasaki, Tadakatsu Ohkubo, Kazuhiro Hono, Yukio Takada, Takashi Sato, Yuji Kaneko, Akira Kato

Acta Materialia　178　(178)　90-98　2019/10
Publisher: Elsevier BV
DOI： 10.1016/j.actamat.2019.08.004 　

ISSN： 1359-6454
Detection of elemental magnetization reversal events in a micro-patterned Nd-Fe-B hot-deformed magnet Peer-reviewed

T. Yomogita, N. Kikuchi, S. Okamoto, O. Kitakami, H. Sepehri-Amin, T. Ohkubo, K. Hono, K. Hioki, A. Hattori

AIP Advances　9　(9)　125052　2019

DOI： 10.1063/1.5129830 　

eISSN： 2158-3226
Microwave-assisted switching in CoCrPt granular medium under continuous microwave fields Peer-reviewed

N. Kikuchi, K. Sato, S. Kikuchi, S. Okamoto, T. Shimatsu, O. Kitakami, H. Osawa, M. Suzuki

JOURNAL OF APPLIED PHYSICS　126　(126)　083908　2019

DOI： 10.1063/1.5111576 　

ISSN： 0021-8979

eISSN： 1089-7550
Microwave-magnetic-field-induced magnetization excitation and assisted switching of antiferromagnetically coupled magnetic bilayer with perpendicular magnetization Peer-reviewed

H. Suto, T. Kanao, T. Nagasawa, K. Mizushima, R. Sato, N. Kikuchi, S. Okamoto

Journal of Applied Physics　125　(125)　153901　2019

DOI： 10.1063/1.5089799 　

ISSN： 0021-8979

eISSN： 1089-7550
First-order reversal curve analysis of a Nd-Fe-B sintered magnet with soft X-ray magnetic circular dichroism microscopy Peer-reviewed

Kazunori Miyazawa, Satoshi Okamoto, Takahiro Yomogita, Nobuaki Kikuchi, Osamu Kitakami, Kentaro Toyoki, David Billington, Yoshinori Kotani, Tetsuya Nakamura, Taisuke Sasaki, Tadakatsu Ohkubo, Kazuhiro Hono

Acta Materialia　162　(162)　1-9　2019/01
Publisher: Elsevier BV
DOI： 10.1016/j.actamat.2018.09.053 　

ISSN： 1359-6454
Confirmation of Hard Magnetic L1(0) FeNi Phase Precipitated in FeNiSiBPCu Alloy by Anomalous X-Ray Diffraction Peer-reviewed

Parmanand Sharma, Satoshi Okamoto, Hiroo Tajiri, Kazuhisa Sato, Yan Zhang, Osamu Kitakami, Akihiro Makino

IEEE TRANSACTIONS ON MAGNETICS　54　(11)　2101705　2018/11

DOI： 10.1109/TMAG.2018.2842057 　

ISSN： 0018-9464

eISSN： 1941-0069
MICROWAVE ASSISTED SWITCHING BEHAVIOR OF COCRPT BASED GRANULAR MEDIA

Nobuaki KIKUCHI, Kyohei SHIMADA, Shun KIKUCHI, Katsunari SATO, Satoshi OKAMOTO, Osamu KITAKAMI, Takehito SHIMATSU

Digest of the 29th Magnetic Recording Conference 2018(TMRC2018)　41-42　2018/08
Microwave Spectroscopy of a Single Permalloy Chiral Metamolecule on a Coplanar Waveguide Peer-reviewed

Toshiyuki Kodama, Yusaku Kusanagi, Satoshi Okamoto, Nobuaki Kikuchi, Osamu Kitakami, Satoshi Tomita, Nobuyoshi Hosoito, Hisao Yanagi

Physical Review Applied　9　(5)　054025　2018/05/17
Publisher: American Physical Society
DOI： 10.1103/PhysRevApplied.9.054025 　

ISSN： 2331-7019
Layer-selective microwave-assisted magnetization switching in a dot of double antiferromagnetically coupled (AFC) layers Peer-reviewed

Yuming Lu, Satoshi Okamoto, Nobuaki Kikuchi, Osamu Kitakami, Takehito Shimatsu

Applied Physics Letters　112　(16)　162404　2018/04/16
Publisher: American Institute of Physics Inc.
DOI： 10.1063/1.5027127 　

ISSN： 0003-6951
Magnetization Reversal of Nd-Fe-B Thin Film under a Nanosecond Pulse Magnetic Field Peer-reviewed

Kazuya Kadonosawa, Nobuaki Kikuchi, Ryota Goto, Satoshi Okamoto, Osamu Kitakami

ELECTRICAL ENGINEERING IN JAPAN　203　(1)　3-8　2018/04

DOI： 10.1002/eej.23057 　

ISSN： 0424-7760

eISSN： 1520-6416
CoCrPt-TiO2グラニュラー薄膜におけるマイクロ波アシスト磁化反転挙動

菊池伸明, 島田恭平, 島津武仁, 岡本聡†, 北上修

電子情報通信学会技術研究報告 MR　117　(501)　45-49　2018/03
Publisher: 電気学会
Temperature and field direction dependences of first-order reversal curve (FORC) diagrams of hot-deformed Nd-Fe-B magnets Peer-reviewed

Takahiro Yomogita, Satoshi Okamoto, Nobuaki Kikuchi, Osamu Kitakami, Hossein Sepehri-Amin, Tadakatsu Ohkubo, Kazuhiro Hono, Takahiro Akiya, Keiko Hioki, Atsushi Hattori

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　447　110-115　2018/02

DOI： 10.1016/j.jmmm.2017.09.072 　

ISSN： 0304-8853

eISSN： 1873-4766
Variation of magnetization dynamics of Co/Ni multilayer by capturing magnetic nanoparticles Peer-reviewed

Y. Otaki, T. Kato, S. Okamoto, N. Kikuchi, D. Oshima, S. Iwata, O. Kitakami

IEEE Transactions on Magnetics　57　6100804　2018
Frequency dependence of microwave-assisted switching in CoCrPt granular perpendicular media Peer-reviewed

N. Kikuchi, K. Shimada, T. Shimatsu, S. Okamoto, O. Kitakami

Japanese Journal of Applied Physics　57　(9)　09TE02　2018

DOI： 10.7567/JJAP.57.09TE02 　

ISSN： 0021-4922

eISSN： 1347-4065
Spin transfer torque switching of Co/Pd multilayers and Gilbert damping of Co-based multilayers Peer-reviewed

T.Kimura, X. Dong, K. Adachi, D. Oshima, T. Kato, Y. Sonobe, S. Okamoto, N. Kikuchi, Y. Kawato, O. Kitakami, S. Iwata

Japanese Journal of Applied Physics　57　(9)　09TD01　2018

DOI： 10.7567/JJAP.57.09TD01 　

ISSN： 0021-4922

eISSN： 1347-4065
Novel torque magnetometry for uniaxial anisotropy constants of thin films and its application to FePt granular thin films Peer-reviewed

T. Ono, N. Kikuchi, S. Okamoto, O. Kitakami, T. Shimatsu

Applied Physics Express　11　(3)　033002　2018

DOI： 10.7567/APEX.11.033002 　

ISSN： 1882-0778

eISSN： 1882-0786
双極子結合した積層磁性ドットによるマイクロ波アシスト実験

金原大樹, 岡本聡, 菊池伸明, 北上修, 島津武仁

電気学会研究会資料　MAGZ43　(234)　21-25　2017/11

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562
双極子結合した積層磁性ドットによるマイクロ波アシス化反転

金原大樹, 岡本聡, 菊池伸明, 北上修, 島津武仁

電子情報通信学会信学技報　MR2017-8　53-58　2017/08

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560
Significant modification of perpendicular magnetic anisotropy of W/Fe(001) multilayer by controlling in-plane lattice constant Peer-reviewed

Yuki Matsumoto, Yoshio Miura, Satoshi Okamoto, Nobuaki Kikuchi, Osamu Kitakami

APPLIED PHYSICS EXPRESS　10　(6)　063005-1-063005-4　2017/06

DOI： 10.7567/APEX.10.063005 　

ISSN： 1882-0778

eISSN： 1882-0786
Influence of intergrain interactions and thermal agitation on microwave-assisted magnetization switching behavior of granular magnetic film Peer-reviewed

Satoshi Okamoto, Nobuaki Kikuchi, Osamu Kitakami, Takehito Shimatsu

APPLIED PHYSICS EXPRESS　10　(2)　023004-1-023004-4　2017/02

DOI： 10.7567/APEX.10.023004 　

ISSN： 1882-0778

eISSN： 1882-0786
Magnetic characteristics and nanostructures of FePt granular films with GeO2 segregant Peer-reviewed

Takuya Ono, Tomohiro Moriya, Masatoshi Hatayama, Kaoru Tsumura, Nobuaki Kikuchi, Satoshi Okamoto, Osamu Kitakami, Takehito Shimatsu

APPLIED PHYSICS LETTERS　110　(2)　2017/01

DOI： 10.1063/1.4973473 　

ISSN： 0003-6951

eISSN： 1077-3118
Magnetization reversal of Nd-Fe-B thin film under a nano-second pulse magnetic field Peer-reviewed

Kazuya Kadonosawa, Nobuaki Kikuchi, Ryota Goto, Satoshi Okamoto, Osamu Kitakami

IEEJ Transactions on Fundamentals and Materials　137　(7)　374-379　2017
Publisher: Institute of Electrical Engineers of Japan
DOI： 10.1541/ieejfms.137.374 　

ISSN： 1347-5533 0385-4205
Addition of Ru to L1(0)-FePt thin film to lower Curie temperature Peer-reviewed

Takuya Ono, Hitoshi Nakata, Tomohiro Moriya, Nobuaki Kikuchi, Satoshi Okamoto, Osamu Kitakami, Takehito Shimatsu

APPLIED PHYSICS EXPRESS　9　(12)　123002-1-123002-3　2016/12

DOI： 10.7567/APEX.9.123002 　

ISSN： 1882-0778

eISSN： 1882-0786
First-order reversal curve analysis in hot-deformed Nd-Fe-B magnets Peer-reviewed

T. Yomogita, S. Okamoto, N. Kikuchi, O. Kitakami, H. Sepehri Amin, T. Ohkubo, K. Hono, T. Akiya, K. Hioki, A. Hattori

REPM 2016 Proceedings　649-653　2016/08/28

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1672
Radio Frequency Field Dependence of Microwave-Assisted Switching Behaviors of Co/Pt Nanodots Peer-reviewed

Masaki Furuta, Satoshi Okamoto, Nobuaki Kikuchi, Osamu Kitakami, Takehito Shimatsu

ELECTRONICS AND COMMUNICATIONS IN JAPAN　99　(8)　79-85　2016/08

DOI： 10.1002/ecj.11842 　

ISSN： 1942-9533

eISSN： 1942-9541
Ferromagnetic Resonance of a Single Magnetochiral Metamolecule of Permalloy Peer-reviewed

Toshiyuki Kodama, Satoshi Tomita, Takeshi Kato, Daiki Oshima, Satoshi Iwata, Satoshi Okamoto, Nobuaki Kikuchi, Osamu Kitakami, Nobuyoshi Hosoito, Hisao Yanagi

PHYSICAL REVIEW APPLIED　6　(2)　024016-1-024016-9　2016/08

DOI： 10.1103/PhysRevApplied.6.024016 　

ISSN： 2331-7019
Magnetics and optics research Peer-reviewed

Hiro Munekata, Yuichi Nakamura, Satoshi Okamoto, Koji Sekiguchi, Yu Shiratsuchi, Masaaki Takezawa

Japanese Journal of Applied Physics　55　(7)　2016/07/01
Publisher: Japan Society of Applied Physics
DOI： 10.7567/JJAP.55.07M001 　

ISSN： 1347-4065 0021-4922
Size dependence of switching behavior in single epitaxial Co/Pt multilayer nanodots Peer-reviewed

Bin Lao, Satoshi Okamoto, Nobuaki Kikuchi, Osamu Kitakami

JAPANESE JOURNAL OF APPLIED PHYSICS　55　(7)　07MC01-1-07MC01-4　2016/07

DOI： 10.7567/JJAP.55.07MC01 　

ISSN： 0021-4922

eISSN： 1347-4065
Magnetic Anisotropy and Crystal Domain Variant in L1(0)-FePt Polycrystalline Films Peer-reviewed

A. Hotta, T. Ono, N. Kikuchi, S. Okamoto, O. Kitakami, T. Shimatsu

IEEE TRANSACTIONS ON MAGNETICS　52　(7)　3200803-1-3200803-3　2016/07

DOI： 10.1109/TMAG.2016.2522504 　

ISSN： 0018-9464

eISSN： 1941-0069
Microwave-Assistance Effect on Magnetization Switching in Antiferromagnetically Coupled CoCrPt Granular Media Peer-reviewed

Y. Nakayama, Y. Kusanagi, T. Shimatsu, N. Kikuchi, S. Okamoto, O. Kitakami

IEEE TRANSACTIONS ON MAGNETICS　52　(7)　3201203-1-3201203-3　2016/07

DOI： 10.1109/TMAG.2015.2507188 　

ISSN： 0018-9464

eISSN： 1941-0069
Magnetization reversal of FePt based exchange coupled composite media Peer-reviewed

J. Wang, H. Sepehri-Amin, Y. K. Takahashi, S. Okamoto, S. Kasai, J. Y. Kim, T. Schrefl, K. Hono

ACTA MATERIALIA　111　47-55　2016/06

DOI： 10.1016/j.actamat.2016.03.001 　

ISSN： 1359-6454

eISSN： 1873-2453
Experimental investigation of off-stoichiometry and 3d transition metal (Mn, Ni, Cu)-substitution in single-crystalline FePt thin films Peer-reviewed

Takuya Ono, Hitoshi Nakata, Tomohiro Moriya, Nobuaki Kikuchi, Satoshi Okamoto, Osamu Kitakami, Takehito Shimatsu

AIP ADVANCES　6　(5)　056011-1-056011-5　2016/05

DOI： 10.1063/1.4943535 　

ISSN： 2158-3226
Simultaneous magnetic and chemical imaging of Nd-Fe-B thin films by means of XMCD-PEEM technique Peer-reviewed

R. Goto, S. Okamoto, T. Ohkochi, N. Kikuchi, O. Kitakami, T. Nakamura

J. Mag. Soc. Jpn　40　(4)　87-90　2016/04
Publisher: The Magnetics Society of Japan
DOI： 10.3379/msjmag.1605R004 　

ISSN： 1882-2924

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8851
Anomalous Hall Effect Measurement on Nanostructure with Magnetic Pulse Fields Peer-reviewed

Nobuaki Kikuchi, Satoshi Okamoto, Osamu Kitakami

MATERIALS TRANSACTIONS　57　(6)　789-795　2016

DOI： 10.2320/matertrans.ME201507 　

ISSN： 1345-9678

eISSN： 1347-5320
Evaluation of damping constants for Co/Pt multilayers and CoPt alloy films Peer-reviewed

Yusaku Kusanagi, Satoshi Okamoto Nobuaki Kikiichi, Osamu Kitakami, Takeshi Kato, Satoshi Iwata

IEEJ Transactions on Fundamentals and Materials　136　(5)　317-323　2016
Publisher: Institute of Electrical Engineers of Japan
DOI： 10.1541/ieejfms.136.317 　

ISSN： 1347-5533 0385-4205
Temperature-dependent magnetization reversal process and coercivity mechanism in Nd-Fe-B hot-deformed magnets Peer-reviewed

Satoshi Okamoto, Ryota Goto, Nobuaki Kikuchi, Osamu Kitakami, Takahiro Akiya, Hossein Sepehri-Amin, Tadakatsu Ohkubo, Kazuhiro Hono, Keiko Hioki, Atsushi Hattori

JOURNAL OF APPLIED PHYSICS　118　(22)　223903-1-223903-9　2015/12

DOI： 10.1063/1.4937274 　

ISSN： 0021-8979

eISSN： 1089-7550
Large Negative Magnetic Anisotropy of W/Fe/W (001) Epitaxial Trilayers Peer-reviewed

Yuki Matsumoto, Satoshi Okamoto, Nobuaki Kikuchi, Osamu Kitakami, Yoshio Miura, Motohiro Suzuki, Masaichiro Mizumaki, Naomi Kawamura

IEEE TRANSACTIONS ON MAGNETICS　51　(11)　2100704　2015/11

DOI： 10.1109/TMAG.2015.2432074 　

ISSN： 0018-9464

eISSN： 1941-0069
Microwave assisted magnetic recording technologies and related physics Invited Peer-reviewed

Satoshi Okamoto, Nobuaki Kikuchi, Masaki Furuta, Osamu Kitakami, Takehito Shimatsu

JOURNAL OF PHYSICS D-APPLIED PHYSICS　48　(35)　353001　2015/09

DOI： 10.1088/0022-3727/48/35/353001 　

ISSN： 0022-3727

eISSN： 1361-6463
Nd-Cu拡散処理をした熱間加工ネオジム磁石のFORC法解析

蓬田貴裕, 菊池伸明, 岡本聡, 北上修, 秋屋貴博, Sepehri-Amin Hossein, 大久保忠勝, 宝野和博, 日置敬子, 服部篤

電気学会マグネティクス研究会資料　MAG-15　(077)　1-4　2015/08

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543
Energy barrier analysis of Nd-Fe-B thin films Peer-reviewed

R. Goto, S. Okamoto, N. Kikuchi, O. Kitakami

JOURNAL OF APPLIED PHYSICS　117　(17)　17B514-1-17B514-4　2015/05

DOI： 10.1063/1.4913940 　

ISSN： 0021-8979

eISSN： 1089-7550
Radio frequency field dependence of microwave assisted switching behaviors of Co/Pt Nanodots Peer-reviewed

Masaki Furuta, Satoshi Okamoto, Nobuaki Kikuchi, Osamu Kitakami, Takehito Shimatsu

IEEJ Transactions on Fundamentals and Materials　135　(4)　229-234　2015/04/01
Publisher: Institute of Electrical Engineers of Japan
DOI： 10.1541/ieejfms.135.229 　

ISSN： 1347-5533 0385-4205
Theoretical study of thermally activated magnetization switching under microwave assistance: Switching paths and barrier height Peer-reviewed

H. Suto, K. Kudo, T. Nagasawa, T. Kanao, K. Mizushima, R. Sato, S. Okamoto, N. Kikuchi, O. Kitakami

PHYSICAL REVIEW B　91　(9)　094401-1-094401-8　2015/03

DOI： 10.1103/PhysRevB.91.094401 　

ISSN： 1098-0121

eISSN： 1550-235X
Energy barrier analysis on hot-deformed Nd-Fe-B magnets. Peer-reviewed

R. Goto, S. Okamoto, T. Akiya, N. Kikuchi, O. Kitakami, H. Sepehri-Amin, T. Ohkubo, K. Hono, K. Hioki, A. Hattori

2015 IEEE MAGNETICS CONFERENCE (INTERMAG)　2015
Quantized spin waves in single Co/Pt dots detected by anomalous Hall effect based ferromagnetic resonance Peer-reviewed

N. Kikuchi, M. Furuta, S. Okamoto, O. Kitakami, T. Shimatsu

APPLIED PHYSICS LETTERS　105　(24)　242405-1-4　2014/12

DOI： 10.1063/1.4904225 　

ISSN： 0003-6951

eISSN： 1077-3118
Granular nanostructures and magnetic characteristics of FePt-TiO2/FePt-C stacked granular films Peer-reviewed

Takuya Ono, Tomohiro Moriya, Masatoshi Hatayama, Nobuaki Kikuchi, Satoshi Okamoto, Osamu Kitakami, Takehito Shimatsu

JOURNAL OF APPLIED PHYSICS　115　(17)　17B709-1-17B709-3　2014/05

DOI： 10.1063/1.4861684 　

ISSN： 0021-8979

eISSN： 1089-7550
Magnetic anisotropy and order structure of L1(0)-FePt(001) single-crystal films grown epitaxially on (001) planes of MgO, SrTiO3, and MgAl2O4 substrates Peer-reviewed

A. Hotta, T. Ono, M. Hatayama, K. Tsumura, N. Kikuchi, S. Okamoto, O. Kitakami, T. Shimatsu

JOURNAL OF APPLIED PHYSICS　115　(17)　17B712-1-17B712-4　2014/05

DOI： 10.1063/1.4862840 　

ISSN： 0021-8979

eISSN： 1089-7550
Size dependence of magnetization switching and its dispersion of Co/Pt nanodots under the assistance of radio frequency fields Peer-reviewed

Masaki Furuta, Satoshi Okamoto, Nobuaki Kikuchi, Osamu Kitakami, Takehito Shimatsu

JOURNAL OF APPLIED PHYSICS　115　(13)　133914-1-133914-8　2014/04

DOI： 10.1063/1.4870451 　

ISSN： 0021-8979

eISSN： 1089-7550
Quasi-ballistic magnetization switching in Co/Pt dots with perpendicular magnetization Peer-reviewed

N. Kikuchi, Y. Suyama, S. Okamoto, O. Kitakami, T. Shimatsu

APPLIED PHYSICS LETTERS　104　(11)　112409-1-112409-4　2014/03

DOI： 10.1063/1.4869150 　

ISSN： 0003-6951

eISSN： 1077-3118
Theory and Experiment of Microwave-Assisted Magnetization Switching in Perpendicular Magnetic Nanodots Invited Peer-reviewed

Satoshi Okamoto, Masaki Furuta, Nobuaki Kikuchi, Osamu Kitakami, Takehito Shimatsu

IEEE TRANSACTIONS ON MAGNETICS　50　(3)　3200906-1-3200906-6　2014/03

DOI： 10.1109/TMAG.2013.2281400 　

ISSN： 0018-9464

eISSN： 1941-0069
Pulse Rise Time Dependence of Switching Field of Co/Pt Multilayer Dot Peer-reviewed

Nobuaki Kikuchi, Yoshihiro Suyama, Satoshi Okamoto, Osamu Kitakami

ELECTRONICS AND COMMUNICATIONS IN JAPAN　96　(12)　9-14　2013/12

DOI： 10.1002/ecj.11569 　

ISSN： 1942-9533

eISSN： 1942-9541
Co/Ptナノドットにおけるマイクロ波アシスト効果のサイズ依存性

古田正樹, 岡本聡, 菊池伸明, 北上修, 島津武仁

電気学会マグネティックス研究会資料　MAG-13-132　2013/12
Microwave assistance effect on magnetization switching in Co-Cr-Pt granular film Peer-reviewed

Satoshi Okamoto, Nobuaki Kikuchi, Akira Hotta, Masaki Furuta, Osamu Kitakami, Takehito Shimatsu

APPLIED PHYSICS LETTERS　103　(20)　202405　2013/11

DOI： 10.1063/1.4830364 　

ISSN： 0003-6951

eISSN： 1077-3118
垂直磁化磁性体におけるマイクロ波アシスト磁化反転

岡本聡

信学技報　CPM2013-4　2013/10
Co/Ptナノドットアレイを用いたマイクロ波アシスト磁化反転実験とその反転挙動解析

古田正樹, 岡本聡, 菊池伸明, 北上修, 島津武仁

電気学会マグネティックス研究会資料　2013　(68)　MAG-13-071-19　2013/08
Co/Ptナノドットアレイを用いたマイクロ波アシスト磁化反転とその反転挙動

古田正樹, 岡本聡, 菊池伸明, 北上修, 島津武仁

信学技報　MR2013-2　2013/06
マイクロ波アシスト磁化反転における解析的考察と実験検証

岡本聡, 菊池伸明, 古田正樹, 北上修, 島津武仁

信学技報　MR2013-5　2013/06
Stoner-Wohlfarth Like Magnetization Switching in Very Small Co/Pt Nanodots under the Assistance of Radio Frequency Magnetic Field Peer-reviewed

Masaki Furuta, Satoshi Okamoto, Nobuaki Kikuchi, Osamu Kitakami, Takehito Shimatsu

APPLIED PHYSICS EXPRESS　6　(5)　053006-1-053006-4　2013/05

DOI： 10.7567/APEX.6.053006 　

ISSN： 1882-0778

eISSN： 1882-0786
High permeability and electromagnetic noise suppression characteristics of Fe-B-P sub-micron particle chains and their composites with NiZn-ferrite nanoparticles Peer-reviewed

Ch. Yao, Y. Shimada, S. Muroga, G. W. Qin, S. Okamoto, O. Kitakami, Y. Endo, M. Yamaguchi

JOURNAL OF ALLOYS AND COMPOUNDS　554　414-418　2013/03

DOI： 10.1016/j.jallcom.2012.11.157 　

ISSN： 0925-8388
Switching Behaviors and its Dynamics of a Co/Pt Nanodot Under the Assistance of rf Fields Peer-reviewed

Satoshi Okamoto, Nobuaki Kikuchi, Masaki Furuta, Osamu Kitakami, Takehito Shimatsu

PHYSICAL REVIEW LETTERS　109　(23)　237209-1-237209-4　2012/12

DOI： 10.1103/PhysRevLett.109.237209 　

ISSN： 0031-9007
Perpendicular Anisotropy and Gilbert Damping in Sputtered Co/Pd Multilayers Peer-reviewed

T. Kato, Y. Matsumoto, S. Kashima, S. Okamoto, N. Kikuchi, S. Iwata, O. Kitakami, S. Tsunashima

IEEE TRANSACTIONS ON MAGNETICS　48　(11)　3288-3291　2012/11

DOI： 10.1109/TMAG.2012.2198446 　

ISSN： 0018-9464
Fabrication of (Co1-xFex)-B Particles With Magnetic Softness Peer-reviewed

Y. Shimada, Y. Endo, M. Yamaguchi, S. Okamoto, O. Kitakami

IEEE TRANSACTIONS ON MAGNETICS　48　(11)　2903-2906　2012/11

DOI： 10.1109/TMAG.2012.2196262 　

ISSN： 0018-9464

eISSN： 1941-0069
マイクロ波アシストにおけるCo/Ptナノドットの磁化反転挙動

岡本聡, 菊池伸明, 古田正樹, 北上修, 島津武仁

日本磁気学会第185回研究会資料　186　5-10　2012/11
Publisher:
ISSN： 1882-2940
Effect of annealing for magnetic softness of Fe-B submicron particles

Y. Shimada, Y. Endo, M. Yamaguchi, S. Okamoto, O. Kitakami

ICAUMS2012 proceedings　12　2012/10/02
Correlation between Switching Field and Microstructure of Individual Co/Pt Dots Peer-reviewed

Nobuaki Kikuchi, Yusuke Murayama, Yasukazu Murakami, Satoshi Okamoto, Daisuke Shindo, Osamu Kitakami

JAPANESE JOURNAL OF APPLIED PHYSICS　51　(10)　103002-1-103002-4　2012/10

DOI： 10.1143/JJAP.51.103002 　

ISSN： 0021-4922
Significant Reduction of Switching Field and its Distribution in Co/Pt Nanodots with Assistance of Radio Frequency Field Peer-reviewed

Satoshi Okamoto, Nobuaki Kikuchi, Masaki Furuta, Osamu Kitakami, Takehito Shimatsu

APPLIED PHYSICS EXPRESS　5　(9)　093005-1-093005-3　2012/09

DOI： 10.1143/APEX.5.093005 　

ISSN： 1882-0778
垂直磁気異方性を有するナノ磁性ドットを用いたマイクロ波アシスト磁化反転

岡本聡, 菊池伸明, 古田正樹, 北上修, 島津武仁

マグネティクス研究会資料　2012/08
Co/Ptナノドットを用いたマイクロ波アシスト磁化反転

岡本聡, 菊池伸明, 古田正樹, 北上修, 島津武仁, 青井基

信学技報　112　(80)　21-24　2012/06
Publisher: The Institute of Electronics, Information and Communication Engineers
ISSN： 0913-5685

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Microwave assisted magnetization switching is implemented for Co/Pt multilayer nanodots. Application of rf fields significantly reduces the switching field of Co/Pt nanodots, and the reduction behavior is similar to that predicted by macrospin simulation. However, some dots are inert to rf fields. These very different switching behaviors may be attributable to a slight difference in the nucleation process of a reversed domain. It is also found that the switching field reduction remains almost constant regardless of the pulse width and interval of rf fields, indicating that the switching event is sufficiently fast and reliable in the ns regime.
Frequency and Time Dependent Microwave Assisted Switching Behaviors of Co/Pt Nanodots Peer-reviewed

Satoshi Okamoto, Nobuaki Kikuchi, Jin Li, Osamu Kitakami, Takehito Shimatsu, Hajime Aoi

APPLIED PHYSICS EXPRESS　5　(4)　043001-1-043001-3　2012/04

DOI： 10.1143/APEX.5.043001 　

ISSN： 1882-0778
Pulse rise time dependence of switching field of Co/Pt multilayer dot Peer-reviewed

Nobuaki Kikuchi, Yoshihiro Suyama, Satoshi Okamoto, Osamu Kitakami

IEEJ Transactions on Fundamentals and Materials　132　(10)　838-843　2012

DOI： 10.1541/ieejfms.132.838 　

ISSN： 0385-4205 1347-5533
Effect of Annealing on Magnetic Properties of Ni80Fe20 Permalloy Nanoparticles Prepared by Polyol Method Peer-reviewed

G. W. Qin, W. L. Pei, Y. P. Ren, Y. Shimada, Y. Endo, M. Yamaguchi, S. Okamoto, O. Kitakami

JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY　11　(12)　10796-10799　2011/12

DOI： 10.1166/jnn.2011.3981 　

ISSN： 1533-4880
Co/Ni多層膜の垂直磁気異方性と時間分解磁化ダイナミクス

加藤剛志, 松本宣大, 岩田聡, 岡本聡, 菊池伸明, 北上修, 綱島滋

電気学会マグネティクス研究会資料　MAG11　(114)　1-6　2011/11
Amorphous Submicron Particle Chains With High Permeability Peer-reviewed

Y. Shimada, Y. Endo, M. Yamaguchi, S. Okamoto, O. Kitakami

IEEE TRANSACTIONS ON MAGNETICS　47　(10)　2831-2834　2011/10

DOI： 10.1109/TMAG.2011.2151181 　

ISSN： 0018-9464
Time-Resolved Magnetization Dynamics and Damping Constant of Sputtered Co/Ni Multilayers Peer-reviewed

T. Kato, Y. Matsumoto, S. Okamoto, N. Kikuchi, O. Kitakami, N. Nishizawa, S. Tsunashima, S. Iwata

IEEE TRANSACTIONS ON MAGNETICS　47　(10)　3036-3039　2011/10

DOI： 10.1109/TMAG.2011.2158082 　

ISSN： 0018-9464
Study of Permeability for Composites Including Fe, NiZn Ferrite and Fe-B-P Particles Peer-reviewed

C. Yao, Y. Shimada, G. W. Qin, W. L. Pei, S. Okamoto, O. Kitakami, Y. Endo, M. Yamaguchi

IEEE TRANSACTIONS ON MAGNETICS　47　(10)　3160-3162　2011/10

DOI： 10.1109/TMAG.2011.2148698 　

ISSN： 0018-9464
Magnetic anisotropy and order parameter for L10 type FePt polycrystalline films with (001) preferred grain orientation Peer-reviewed

D. Inoue, T. Shimatsu, Y. Inaba, H. Aoi, S. Okamoto, O. Kitakami

Journal of Applied Physics　in press　2011/09

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6722
Temperature dependence of the magnetic properties of L1(1)-type Co-Ni-Pt ordered alloy films for thermally assisted recording media Peer-reviewed

Junichi Sayama, Takehito Shimatsu, Hiroaki Nemoto, Satoshi Okamoto, Osamu Kitakami, Hajime Aoi

JOURNAL OF APPLIED PHYSICS　110　(1)　013918　2011/07

DOI： 10.1063/1.3608123 　

ISSN： 0021-8979
Dot arrays of L1(0)-type FePt ordered alloy perpendicular films fabricated using low-temperature sputter film deposition Peer-reviewed

T. Shimatsu, Y. Inaba, H. Kataoka, J. Sayama, H. Aoi, S. Okamoto, O. Kitakami

JOURNAL OF APPLIED PHYSICS　109　(7)　07B726　2011/04

DOI： 10.1063/1.3556697 　

ISSN： 0021-8979
Microwave assisted magnetization switching in Co/Pt multilayer Peer-reviewed

S. Okamoto, N. Kikuchi, O. Kitakami, T. Shimatsu, H. Aoi

JOURNAL OF APPLIED PHYSICS　109　(7)　07B748　2011/04

DOI： 10.1063/1.3561780 　

ISSN： 0021-8979
Uniform Magnetic Dot Fabrication by Nanoindentation Lithography Peer-reviewed

Nobuaki Kikuchi, Tomohiko Hashimoto, Satoshi Okamoto, Ze Shen, Osamu Kitakami

JAPANESE JOURNAL OF APPLIED PHYSICS　50　(4)　046505　2011/04

DOI： 10.1143/JJAP.50.046505 　

ISSN： 0021-4922

eISSN： 1347-4065
Co/Pt multilayer dot switching experiments with sub-nanosecond pulse field Peer-reviewed

N. Kikuchi, Y. Suyama, S. Okamoto, O. Kitakami

JOURNAL OF APPLIED PHYSICS　109　(7)　07B904　2011/04

DOI： 10.1063/1.3540405 　

ISSN： 0021-8979
Magnetization Reversal of Single Co/Pd Multilayer Nanodot by Nanoseconds Pulse Field Peer-reviewed

Y. Suyama, Y. Murayama, N. Kikuchi, S. Okamoto, O. Kitakami

2ND INTERNATIONAL SYMPOSIUM ON ADVANCED MAGNETIC MATERIALS AND APPLICATIONS (ISAMMA 2010)　266　012083　2011

DOI： 10.1088/1742-6596/266/1/012083 　

ISSN： 1742-6588
Microwave assisted switching mechanism and its stable switching limit Peer-reviewed

S. Okamoto, M. Igarashi, N. Kikuchi, O. Kitakami

JOURNAL OF APPLIED PHYSICS　107　(12)　2010/06

DOI： 10.1063/1.3436570 　

ISSN： 0021-8979
Synthesis and magnetic softness of submicron amorphous particles Peer-reviewed

Y. Shimada, Y. Endo, M. Yamaguchi, S. Okamoto, O. Kitakami, Y. Imano, H. Masumoto, S. Yoshida

Journal of the Magnetics Society of Japan　34　(3)　220-225　2010/06
Publisher: The Magnetics Society of Japan
DOI： 10.3379/msjmag.1003R053 　

ISSN： 1882-2924

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6173
Effect of dipole interaction on microwave assisted magnetization switching Peer-reviewed

S. Okamoto, N. Kikuchi, O. Kitakami, M. Igarashi

JOURNAL OF APPLIED PHYSICS　107　(3)　2010/02

DOI： 10.1063/1.3298929 　

ISSN： 0021-8979
Effect of Annealing on Magnetic Properties of Ni80Fe20 Permalloy Nanoparticles with Various Sizes Prepared by Polyol Method Peer-reviewed

G. W. Qin, W. L. Pei, Y. P. Ren, Y. Shimada, Y. Endo, M. Yamaguchi, S. Okamoto, O. Kitakami

INEC: 2010 3RD INTERNATIONAL NANOELECTRONICS CONFERENCE, VOLS 1 AND 2　1116-+　2010
Magnetic anisotropy of L1(1)-type (Co1-XMX)(50)Pt-50 (M:Ni, Fe, Cr, Mn) and Co-50(Pt1-XPdX)(50) ordered alloy perpendicular films Peer-reviewed

H. Kataoka, H. Sato, T. Shimatsu, S. Okamoto, O. Kitakami, H. Aoi

INTERNATIONAL CONFERENCE ON MAGNETISM (ICM 2009)　200　(10)　102002(4pp)　2010

DOI： 10.1088/1742-6596/200/10/102002 　

ISSN： 1742-6588
Remanence coercivity of dot arrays of hcp-CoPt perpendicular films Peer-reviewed

K. Mitsuzuka, T. Shimatsu, N. Kikuchi, S. Okamoto, H. Aoi, O. Kitakami

INTERNATIONAL CONFERENCE ON MAGNETISM (ICM 2009)　200　102005　2010

DOI： 10.1088/1742-6596/200/10/102005 　

ISSN： 1742-6588
Magnetic and structural properties of L1(1) type CoPt-C ordered alloy perpendicular films as a function of C content Peer-reviewed

T. Shimatsu, H. Sato, H. Kataoka, S. Okamoto, O. Kitakami, H. Aoi

INTERNATIONAL CONFERENCE ON MAGNETISM (ICM 2009)　200　(SECTION 10)　102008　2010

DOI： 10.1088/1742-6596/200/10/102008 　

ISSN： 1742-6588
Ni80Fe20 permalloy nanoparticles: Wet chemical preparation, size control and their dynamic permeability characteristics when composited with Fe micron particles Peer-reviewed

G. W. Qin, W. L. Pei, Y. P. Ren, Y. Shimada, Y. Endo, M. Yamaguchi, S. Okamoto, O. Kitakami

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　321　(24)　4057-4062　2009/12

DOI： 10.1016/j.jmmm.2009.08.004 　

ISSN： 0304-8853
Bistability Condition of Circular Nanomagnet Peer-reviewed

Osamu Kitakami, Satoshi Okamoto, Nobuaki Kikuchi, Takehito Shimatsu, Kaname Mitsuzuka, Hajime Aoi

APPLIED PHYSICS EXPRESS　2　(12)　123002　2009/12

DOI： 10.1143/APEX.2.123002 　

ISSN： 1882-0778
Production of Magnetically Soft Submicron Particles From Aqueous Solutions and Characterization Peer-reviewed

Y. Shimada, Y. Endo, M. Yamaguchi, S. Okamoto, O. Kitakami, Y. Imano, H. Matsumoto, S. Yoshida

IEEE TRANSACTIONS ON MAGNETICS　45　(10)　4298-4301　2009/10

DOI： 10.1109/TMAG.2009.2024951 　

ISSN： 0018-9464
Ferromagnetic resonance of Co/Ni multilayer Peer-reviewed

S. Okamoto, F. Ono, N. Kikuchi, O. Kitakami, Y. Mitsuzuka, Y. Endo, M. Yamaguchi

International Conference on Magnetism (ICM 2009) Abstracts　191　2009/07
Magnetic anisotropy of epitaxially grown Co and its alloy thin films Peer-reviewed

J-J Wang, T. Sakurai, K. Oikawa, K. Ishida, N. Kikuchi, S. Okamoto, H. Sato, T. Shimatsu, O. Kitakami

JOURNAL OF PHYSICS-CONDENSED MATTER　21　(18)　185008/1-185008/6　2009/05

DOI： 10.1088/0953-8984/21/18/185008 　

ISSN： 0953-8984
Fabrication of L1(1)-type (Co-Ni)-Pt ordered alloy films by sputter deposition Peer-reviewed

H. Sato, T. Shimatsu, H. Kataoka, H. Aoi, S. Okamoto, O. Kitakami

JOURNAL OF APPLIED PHYSICS　105　(7)　2009/04

DOI： 10.1063/1.3072758 　

ISSN： 0021-8979
Generation of nanosecond magnetic pulse field for switching experiments on a single Co/Pt nanodot Peer-reviewed

N. Kikuchi, S. Okamoto, O. Kitakami

JOURNAL OF APPLIED PHYSICS　105　(7)　2009/04

DOI： 10.1063/1.3061964 　

ISSN： 0021-8979
Dot arrays of L1(1) type Co-Pt ordered alloy perpendicular films Peer-reviewed

T. Shimatsu, H. Sato, K. Mitsuzuka, H. Kataoka, H. Aoi, S. Okamoto, O. Kitakami

JOURNAL OF APPLIED PHYSICS　105　(7)　2009/04

DOI： 10.1063/1.3068539 　

ISSN： 0021-8979
記録材料のナノサイズ領域における磁化挙動の検討 Peer-reviewed

北上修, 岡本聡, 菊池伸明, 島津武仁, 佐藤英夫, 三塚要, 青井基

日本磁気学会第165回研究会資料「極限状態の磁気ストレージ」　1-8　2009/03
Magnetic behavior of single nanostructured magnet Invited Peer-reviewed

O. Kitakami, S. Okamoto, N. Kikuchi, T. Shimatsu, H. Sato, H. Aoi

Journal of Physics: Conference Series　165　(012029)　2009
Publisher: Institute of Physics Publishing
DOI： 10.1088/1742-6596/165/1/012029 　

ISSN： 1742-6596 1742-6588
Large negative magnetic anisotropy in epitaxially grown Fe/Co multilayer films Peer-reviewed

S. Okamoto, T. Shinozaki, T. Yamashita, N. Kikuchi, O. Kitakami

Journal of the Magnetics Society of Japan　33　(6)　451-454　2009
Publisher: The Magnetics Society of Japan
DOI： 10.3379/msjmag.0907MC0001 　

ISSN： 1882-2924

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5714
Initial permeability of magnetically soft particles with composite structure Peer-reviewed

Y. Shimada, Y. Endo, M. Yamaguchi, S. Okamoto, O. Kitakami

Journal of the Magnetics Society of Japan　33　(2)　95-99　2009
Publisher: The Magnetics Society of Japan (MSJ)
DOI： 10.3379/msjmag.0901RD8002 　

ISSN： 1882-2924

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5540
Magnetization Switching Experiments on Sub-Micron Co/Pt Multilayer Dot Using a Pulse Field Generator With Nanoseconds Duration Peer-reviewed

Atsuo Ito, Nobuaki Kikuchi, Satoshi Okamoto, Osamu Kitakami

IEEE TRANSACTIONS ON MAGNETICS　44　(11)　3446-3449　2008/11

DOI： 10.1109/TMAG.2008.2002630 　

ISSN： 0018-9464
Magnetization behavior of nanomagnets for patterned media application Invited Peer-reviewed

S. Okamoto, N. Kikuchi, T. Kato, O. Kitakami, K. Mitsuzuka, T. Shimatsu, H. Muraoka, H. Aoi, J. C. Lodder

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　320　(22)　2874-2879　2008/11

DOI： 10.1016/j.jmmm.2008.07.034 　

ISSN： 0304-8853
Thermal stability and switching field of hard/soft-stacked perpendicular media Peer-reviewed

T. Shimatsu, N. Asakura, Y. Inaba, K. Kudo, A. Sato, H. Muraoka, H. Aoi, S. Okamoto, O. Kitakami

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　320　(22)　3088-3091　2008/11

DOI： 10.1016/j.jmmm.2008.08.020 　

ISSN： 0304-8853
Frequency modulation effect on microwave assisted magnetization switching Peer-reviewed

S. Okamoto, N. Kikuchi, O. Kitakami

APPLIED PHYSICS LETTERS　93　(14)　142501　2008/10

DOI： 10.1063/1.2996573 　

ISSN： 0003-6951
大きな垂直磁気異方性を有する磁性薄膜の形成とビット・パターン媒体への応用 Peer-reviewed

島津武仁, 佐藤英夫, 青井基, 岡本聡, 北上修

応用物理学会研究会資料「スピントロニクスの基礎と応用」p.1-p.6　2008/10
Magnetization switching behavior with microwave assistance Peer-reviewed

S. Okamoto, N. Kikuchi, O. Kitakami

APPLIED PHYSICS LETTERS　93　(10)　102506　2008/09

DOI： 10.1063/1.2977474 　

ISSN： 0003-6951
High frequency permeability of fine particle composites Invited Peer-reviewed

Y. Shimada, Y. Endo, M. Yamaguchi, S. Okamoto, O. Kitakami

6th International Workshop on High Frequency Micormagnetic Devices and Materials (MMDM6)　4-5　2008/05/09
Energy barrier and reversal mechanism in Co/Pt multilayer nanodot Peer-reviewed

S. Okamoto, T. Kato, N. Kikuchi, O. Kitakami, N. Tezuka, S. Sugimoto

JOURNAL OF APPLIED PHYSICS　103　(7)　07C501 /1-3　2008/04

DOI： 10.1063/1.2831785 　

ISSN： 0021-8979
Magnetization reversal process and bistability of Co/Pt multilayer dot Peer-reviewed

N. Kikuchi, T. Kato, S. Okamoto, O. Kitakami, N. Tezuka, S. Sugimoto

JOURNAL OF APPLIED PHYSICS　103　(7)　07C510 /1-3　2008/04

DOI： 10.1063/1.2838288 　

ISSN： 0021-8979
The critical size between single domain and multidomain in L1(0)-FePt particles Peer-reviewed

N. Kikuchi, S. Okamoto, O. Kitakami

JOURNAL OF APPLIED PHYSICS　103　(7)　07D511 /1-3　2008/04

DOI： 10.1063/1.2830679 　

ISSN： 0021-8979
Fabrication of L1(1) type Co-Pt ordered alloy films by sputter deposition Peer-reviewed

H. Sato, T. Shimatsu, Y. Okazaki, H. Muraoka, H. Aoi, S. Okamoto, O. Kitakami

JOURNAL OF APPLIED PHYSICS　103　(7)　07E114 /1-3　2008/04

DOI： 10.1063/1.2830097 　

ISSN： 0021-8979
Uniaxial magnetic anisotropy in Co and Co-Pt based perpendicular films in relation to lattice deformation Peer-reviewed

T. Shimatsu, Y. Okazaki, H. Sato, H. Muraoka, H. Aoi, T. Sakurai, S. Okamoto, O. Kitakami, S. Tanii, A. Sakuma

JOURNAL OF APPLIED PHYSICS　103　(7)　07F524 /1-3　2008/04

DOI： 10.1063/1.2835448 　

ISSN： 0021-8979
Magnetization behavior of nanomagnets for patterned media application

S. Okamoto, N. Kikuchi, O. Kitakami, T. Shimatsu

IEICE Technical Report　107　(324)　7-12　2007/11/09
Publisher: The Institute of Electronics, Information and Communication Engineers
ISSN： 1342-6893

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MR2007-27
Recording resolution and writability for (Co-Pt)-SiO2/Co-SiO2 hard/soft-stacked granular perpendicular media Peer-reviewed

T. Shimatsu, Y. Inaba, S. Watanabe, O. Kitakami, S. Okamoto, H. Aoi, H. Muraoka, Y. Nakamura

IEEE TRANSACTIONS ON MAGNETICS　43　(6)　2103-2105　2007/06

DOI： 10.1109/TMAG.2007.892539 　

ISSN： 0018-9464
Magnetic anisotropy of Co-M-Pt (M = Cr, Mo, Ru, W, Re) perpendicular films denosited on various eed laver materials Peer-reviewed

H. Sato, T. Shimatsu, Y. Okazaki, O. Kitakami, S. Okamoto, H. Aoi, Muraoka, Y. Nakamura

IEEE TRANSACTIONS ON MAGNETICS　43　(6)　2106-2108　2007/06

DOI： 10.1109/TMAG.2007.892540 　

ISSN： 0018-9464

eISSN： 1941-0069
Large uniaxial magnetic anisotropy of Co-Pt perpendicular films induced by lattice deformation Peer-reviewed

T. Shimatsu, Y. Okazaki, H. Sato, O. Kitakami, S. Okamoto, H. Aoi, H. Muraoka, Y. Nakamura

IEEE TRANSACTIONS ON MAGNETICS　43　(6)　2995-2997　2007/06

DOI： 10.1109/TMAG.2007.893126 　

ISSN： 0018-9464
Permeability of submicron and nanometer ferromagnetic particle composites Peer-reviewed

Y. Shimada, M. Yamaguchi, G. W. Qin, S. Okamoto, O. Kitakami

JOURNAL OF APPLIED PHYSICS　101　(9)　09M505-1-09M505-3　2007/05

DOI： 10.1063/1.2712019 　

ISSN： 0021-8979
Epitaxially grown L1(0)-FePt/(C, SiO2, and Al2O3) granular films Peer-reviewed

Satoshi Okamoto, Osamu Kitakami

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　310　(2)　2367-2368　2007/03

DOI： 10.1016/j.jmmm.2006.11.108 　

ISSN： 0304-8853

eISSN： 1873-4766
パターン媒体用磁性材料 -パターン媒体による5 Tbpsi実現可能性について- Peer-reviewed

北上修, 岡本聡, 菊池伸明

電子情報技術産業協会(JEITA) 『ストレージ技術調査研究報告書Ⅰ』　21-32　2007/03
Magnetic properties of Hard/Soft stacked perpendicular media having very thin soft layers with a high saturation magnetization Peer-reviewed

Y. Inaba, T. Shimatsu, S. Watanabe, O. Kitakami, S. Okamoto, H. Muraoka, H. Aoi, Y. Nakamura

Journal of the Magnetics Society of Japan　31　(3)　178-183　2007
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.31.178 　

ISSN： 0285-0192

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4388
単一ナノ磁性体の磁化反転およびそのダイナミクス Peer-reviewed

岡本聡, 加藤貴裕, 伊藤淳郎, 菊池伸明, 北上修

電気学会マグネティクス研究会資料　MAG07　(33)　1-5　2007
Magnetic properties to optimize the K-u2 effect in perpendicular recording media Peer-reviewed

Hideo Sato, Takehito Shimatsu, Takeshi Kondo, Sadayuki Watanabe, Osamu Kitakami, Satoshi Okamoto, Hajime Aoi, Hiroaki Muraoka, Yoshihisa Nakamura

IEEE TRANSACTIONS ON MAGNETICS　42　(10)　2387-2389　2006/10

DOI： 10.1109/TMAG.2006.878668 　

ISSN： 0018-9464
Magnetization reversal of FePt hard/soft stacked nanocomposite particle assembly Peer-reviewed

Y. K. Takahashi, K. Hono, S. Okamoto, O. Kitakami

JOURNAL OF APPLIED PHYSICS　100　(7)　74305　2006/10

DOI： 10.1063/1.2355442 　

ISSN： 0021-8979
Metamagnetic shape memory effect in a Heusler-type Ni43Co7Mn39Sn11 polycrystalline alloy Peer-reviewed

R Kainuma, Y Imano, W Ito, H Morito, Y Sutou, K Oikawa, A Fujita, K Ishida, S Okamoto, O Kitakami

APPLIED PHYSICS LETTERS　88　(19)　192513　2006/05

DOI： 10.1063/1.2203211 　

ISSN： 0003-6951
CoPtCr-SiO2 media with K-u2 magnetic anisotropy term fabricated with Pd seed layers Peer-reviewed

H. Sato, T. Shimatsu, T. Kondo, S. Watanabe, H. Aoi, H. Muraoka, Y. Nakamura, S. Okamoto, O. Kitakami

JOURNAL OF APPLIED PHYSICS　99　(8)　08G907　2006/04

DOI： 10.1063/1.2166587 　

ISSN： 0021-8979

eISSN： 1089-7550
Large uniaxial magnetic anisotropy by lattice deformation in CoPt/Ru perpendicular films Peer-reviewed

T. Shimatsu, H. Sato, Y. Okazaki, H. Aoi, H. Muraoka, Y. Nakamura, S. Okamoto, O. Kitakami

JOURNAL OF APPLIED PHYSICS　99　(8)　08G908　2006/04

DOI： 10.1063/1.2167351 　

ISSN： 0021-8979

eISSN： 1089-7550
Structural and magnetic properties in annealed FePt-B-x (x=0.05 and 0.33) thin films Peer-reviewed

Y. M.Lee, B. S. Lee, C. G. Lee, B. H. Koo, Y. Shimada, O. Kitakami, S. Okamoto, T. Miyazaki

Journal of Korean Physical Society　49　1034　2006/04
Effect of magnetic field on martensitic transition of Ni46Mn41In13 Heusler alloy Peer-reviewed

K Oikawa, W Ito, Y Imano, Y Sutou, R Kainuma, K Ishida, S Okamoto, O Kitakami, T Kanomata

APPLIED PHYSICS LETTERS　88　(12)　122507　2006/03

DOI： 10.1063/1.2187414 　

ISSN： 0003-6951
Magnetic-field-induced shape recovery by reverse phase transformation Peer-reviewed

R Kainuma, Y Imano, W Ito, Y Sutou, H Morito, S Okamoto, O Kitakami, K Oikawa, A Fujita, T Kanomata, K Ishida

NATURE　439　(7079)　957-960　2006/02

DOI： 10.1038/nature04493 　

ISSN： 0028-0836
複合微粒子集合体の初透磁率 Peer-reviewed

島田寛, 山口正洋, 岡本聡, 北上修, G.W. Qin, 及川勝成

日本応用磁気学会誌　30　(6-1)　2006

DOI： 10.3379/jmsjmag.30.540 　

ISSN： 0285-0192
Interfacilly disordered FePt hard/soft stacked structures Peer-reviewed

Y. K. Takahashi, K. Hono, S. Okamoto, O. Kitakami

INTERMAG 2006 - IEEE International Magnetics Conference　255　2006

DOI： 10.1109/INTMAG.2006.375837 　
Large uniaxial magnetic anisotropy in Co100-xPtx/Ru disordered perpendicular films Peer-reviewed

T. Shimatsu, Y. Okazaki, H. Sato, O. Kitakami, S. Okamoto, H. Aoi, H. Muraoka, Y. Nakamura

INTERMAG 2006 - IEEE International Magnetics Conference　169　2006

DOI： 10.1109/INTMAG.2006.375669 　
Enhanced initial permeability of composite assembly of ferromagnetic particles Peer-reviewed

Y. Shimada, M. Yamaguchi, S. Okamoto, O. Kitakami, G. W. Qin, K. Oikawa

INTERMAG 2006 - IEEE International Magnetics Conference　30　510　2006

DOI： 10.1109/INTMAG.2006.376234 　
Coercivity control of FePt nanoparticles by interfacial disorder Peer-reviewed

Y. K. Takahashi, S. Okamoto, O. Kitakami, Y. Shimada, K. Hono

Materials Transactions　47　(1)　38-42　2006/01

DOI： 10.2320/matertrans.47.38 　

ISSN： 1345-9678
Additive effects of AlN and MgO on FePt nanoparticle assembly Peer-reviewed

Satoshi Okamoto, Osamu Kitakami, Yutaka Shimada

Materials Transactions　47　(1)　43-46　2006/01

DOI： 10.2320/matertrans.47.43 　

ISSN： 1345-9678
Size effect on the ordering of L1(0) FePt nanoparticles Peer-reviewed

T Miyazaki, O Kitakami, S Okamoto, Y Shimada, Z Akase, Y Murakami, D Shindo, YK Takahashi, K Hono

PHYSICAL REVIEW B　72　(14)　2005/10

DOI： 10.1103/PhysRevB.72.144419 　

ISSN： 1098-0121

eISSN： 1550-235X
CoPtCr-SiO2 perpendicular media for high density recording with a high order magnetic anisotropy energy term Peer-reviewed

T Shimatsu, H Sato, T Oikawa, K Mitsuzuka, Y Inaba, O Kitakami, S Okamoto, H Aoi, H Muraoka, Y Nakamura

IEEE TRANSACTIONS ON MAGNETICS　41　(10)　3175-3177　2005/10

DOI： 10.1109/TMAG.2005.855282 　

ISSN： 0018-9464

eISSN： 1941-0069
Magnetic softness of permalloy granular films produced by co-evaporation Peer-reviewed

T Itoh, Y Shimada, S Yoshida, S Okamoto, O Kitakami, D Shindo, Y Murakami, JH Yoo

IEEE TRANSACTIONS ON MAGNETICS　41　(10)　3274-3276　2005/10

DOI： 10.1109/TMAG.2005.854900 　

ISSN： 0018-9464
Magnetization reversal process in FePt L1(0) nanoparticles Peer-reviewed

S Okamoto, N Kikuchi, O Kitakami, Y Shimada

SCRIPTA MATERIALIA　53　(4)　395-401　2005/08

DOI： 10.1016/j.scriptamat.2005.04.034 　

ISSN： 1359-6462
K-u2 magnetic anisotropy term of CoPtCr-SiO2 media for high density recording Peer-reviewed

T Shimatsu, H Sato, K Mitsuzuka, T Oikawa, Y Inaba, H Aoi, H Muraoka, Y Nakamura, O. Kitakami, S. Okamoto

JOURNAL OF APPLIED PHYSICS　97　(10)　2005/05

DOI： 10.1063/1.1851918 　

ISSN： 0021-8979

eISSN： 1089-7550
Ku2 term of magnetic anisotropy and microstructure of CoPtCr-SiO2 perpendicular recording media Peer-reviewed

H. Sato, T. Shimatsu, K. Mitsuzuka, T. Oikawa, O. Kitakami, S. Okamoto, H. Muraoka, H. Aoi, Y. Nakamura

Journal of The Magnetics Society of Japan　29　(4)　427-431　2005/04
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.29.427 　

ISSN： 0285-0192

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The higher energy term of magnetic anisotropy, K_u2, which is theoretically predicted to enhance thermal stability without a notable change in switching field, is discussed for CoPtCr-SiO₂ perpendicular recording media. CoPtCr films deposited on Ru seed layers show a high value of the first order energy term, K_u1. The K_u1 value reaches 1.3 × 10⁷ erg/cm³ for Co₇₀Pt₃₀ composition, for instance, whereas the K_u2 values were found to be negligibly small irrespective of the film composition. However, it was revealed that the values of K_u1 and K_u2 vary significantly according to the seed layer material used. K_u2 increases as the c/a of hcp-CoPtCr lattice of the film increases, whereas K_u1 decreases as the c/a increases. This result implies that the appearance of K_u2 is related to the elongation of the hcp-lattice or an increase in the stacking fault density. The addition of SiO₂ to the CoPtCr films reduces the values of K_u1 and K_u2, however, no significant change in the value of K_u2/K_u1 was observed on the addition of SiO₂ to CoCrPt films. It was concluded that CoPtCr-SiO₂ films have a sufficient potential in the values of K_u1 and K_u2 for high-density perpendicular media.
High-potential magnetic anisotropy of CoPtCr-SiO2 perpendicular recording media Peer-reviewed

T Shimatsu, H Sato, T Oikawa, Y Inaba, O Kitakami, S Okamoto, H Aoi, H Muraoka, Y Nakamura

IEEE TRANSACTIONS ON MAGNETICS　41　(2)　566-571　2005/02

DOI： 10.1109/TMAG.2004.838071 　

ISSN： 0018-9464

eISSN： 1941-0069
Effect of boron additon on the ordering process in the FePt thin film

Chan-Gyu Lee, Byeong-Seon Lee, Y. Shimada, O. Kitakami, S. Okamoto, T. Miyazaki

INTERMAG ASIA 2005: Digests of the IEEE International Magnetics Conference　433　2005
Quantitative analysis of ordering of equiatomic FePt nanoparticles by electron diffraction Peer-reviewed

T. Miyazaki, Y. K. Takahashi, S. Okamoto, O. Kitakami, Y. Shimada, Z. Akase, Y. Murakami, D. Shindo, K. Hono

INTERMAG ASIA 2005: Digests of the IEEE International Magnetics Conference　86　2005
Assembly of FePt L1(0) nanoparticles grown on MgO(110) with self-organized groove structure Peer-reviewed

S Okamoto, O Kitakami, T Miyazaki, Y Shimada, YK Takahashi, K Hono

JOURNAL OF APPLIED PHYSICS　96　(9)　5217-5221　2004/11

DOI： 10.1063/1.1794903 　

ISSN： 0021-8979

eISSN： 1089-7550
Direct observation of magnetically induced phase separation in Co-W sputtered thin films Peer-reviewed

K Oikawa, GW Qin, M Sato, S Okamoto, O Kitakami, Y Shimada, K Fukamichi, K Ishida, T Koyama

APPLIED PHYSICS LETTERS　85　(13)　2559-2561　2004/09

DOI： 10.1063/1.1793354 　

ISSN： 0003-6951
High perpendicular magnetic anisotropy of CoPtCr/Ru films for granular-type perpendicular media Peer-reviewed

T Shimatsu, H Sato, T Oikawa, Y Inaba, O Kitakami, S Okamoto, H Aoi, H Muraoka, Y Nakamura

IEEE TRANSACTIONS ON MAGNETICS　40　(4)　2483-2485　2004/07

DOI： 10.1109/tmag.2004.832448 　

ISSN： 0018-9464

eISSN： 1941-0069
RF permeability of the fiber structure in ferromagnetic metal/oxide films deposited by co-evaporation Peer-reviewed

T Itoh, Y Shimada, S Okamoto, O Kitakami

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　272　1419-1420　2004/05

DOI： 10.1016/j.jmmm.2004.01.068 　

ISSN： 0304-8853
Observation of magnetic domain structure in FePt(001) films by electron holography and lorentz microscopy Peer-reviewed

Tomokazu Hino, Yasukazu Murakami, Daisuke Shindo, Satoshi Okamoto, Osamu Kitakami, Yutaka Shimada

Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals　68　(5)　315-319　2004/05

DOI： 10.2320/jinstmet.68.315 　

ISSN： 0021-4876
High perpendicular magnetic anisotropy of CoPtCr-SiO2 perpendicular recording media Peer-reviewed

T. Shimatsu, H. Sato, T. Oikawa, Y. Inaba, O. Kitakami, S. Okamoto, H. Aoi, H. Muraoka, Y. Nakamura

IEEE Transactions on Magnetics　40　2483-2485　2004/04
ZnO下地上におけるL10 FePt (001)優先成長 Peer-reviewed

桜井伴明, 猪狩佳幸, 岡本聡, 北上修, 島田寛

日本応用磁気学会誌　27　(2)　136-140　2004/04
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.28.136 　

ISSN： 0285-0192

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We investigated the effects of ZnO underlayers on the crystal orientation of L1₀ FePt polycrystalline films and found that thin ZnO underlayers with good c-axis orientation promote preferential growth of FePt (001) in spite of their different crystal lattice symmetry, resulting in excellent perpendicular magnetic properties. This unexpected result was qualitatively explained by the proposed model for lattice matching between ZnO (00·l) and FePt (001). Annealing at temperatures above 550°C, however, gives rise to chemical reactions at the FePt/ZnO and ZnO/substrate (in this case Si) interfaces, causing severe reduction of the magnetic moment of FePt and/or changes in the film morphology. Therefore, heating processes above 550°C should be avoided when we use ZnO as the underlayer material for promotion of FePt (001) orientation.
Co-Mo, W合金薄膜における磁気相分離 Peer-reviewed

佐藤公宣, 及川勝成, 岡本聡, 北上修, 島田寛

日本応用磁気学会誌　28　245-248　2004/04

DOI： 10.3379/jmsjmag.28.245 　
L10 FePt (001) c軸配向の熱処理条件依存性 Peer-reviewed

藤慶彦, 岡本聡, 北上修, 島田寛, 小池淳一

日本応用磁気学会誌　28　(3)　376-379　2004/04
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.28.376 　

ISSN： 0285-0192

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We studied the c-axis direction and ordering process of L1₀-FePt thin films during thermal annealing. For the thinner (5 and 10 nm) samples, rapid annealing clearly promoted (001) orientation with higher L1₀ ordering. However, for the thicker (50 nm) samples, (111) orientation was dominant independent of the annealing conditions. We suggest that stress direction and its relaxation during thermal annealing strongly relate to these remarkable changes of orientation and L1₀-ordering.
(Ni80Fe20)-(B2O3)共蒸着薄膜の微細構造と電磁ノイズ抑制効果 Peer-reviewed

伊藤哲夫, 吉田栄吉, 岡本聡, 北上修, 島田寛

日本応用磁気学会誌　28　(3)　401-404　2004/04
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.28.401 　

ISSN： 0285-0192

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It has been verified that high permeability granular films work as RF electromagnetic noise absorbers when they are placed in the vicinity of electronic devices radiating RF noise. However their limited resistivity induces eddy current that re-radiates RF noise back to the source. In this paper it is reported that thin films produced by co-evaporation of Ni₈₀Fe₂₀ and B₂O₃ have a very thin columnar structure that leads to a very high resistivity. The nano-structure is an assembly of thin columns that have a perpendicular anisotropy with the hard axis in the in-plane direction. The films exhibit a remarkable feature as RF noise absorbers that are equivalent to the conventional noise absorbing sheets that are 50 times thicker than the films.
ナノ磁性粒子の磁化反転機構 Peer-reviewed

岡本聡, 菊池伸明, 北上修, 島田寛

日本金属学会報まてりあ　43　(9)　737-743　2004/04
Publisher: The Japan Institute of Metals and Materials
DOI： 10.2320/materia.43.737 　

ISSN： 1340-2625
The anisotropy field of FePt L1(0) nanoparticles controlled by very thin Pt layer Peer-reviewed

S Okamoto, O Kitakami, N Kikuchi, T Miyazaki, Y Shimada, TH Chiang

JOURNAL OF PHYSICS-CONDENSED MATTER　16　(12)　2109-2114　2004/03

DOI： 10.1088/0953-8984/16/12/020 　

ISSN： 0953-8984

eISSN： 1361-648X
Sharrock relation for perpendicular recording media with higher-order magnetic anisotropy terms Peer-reviewed

O Kitakami, T Shimatsu, S Okamoto, Y Shimada, H Aoi

JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS　43　(1A-B)　L115-L117　2004/01

DOI： 10.1143/JJAP.43.L115 　

ISSN： 0021-4922
Large perpendicular magnetic anisotropy of CoPtCr/Ru films for granular-type perpendicular media Peer-reviewed

T. Shimatsu, H. Sato, T. Oikawa, Y. Inaba, O. Kitakami, S. Okamoto, H. Aoi, H. Muraoka, Y. Nakamura

Digests of International Symposium on Ultra-High Density Spinic Storage Systems　(PS-19)　68-69　2003/10/30
Magnetic Anisotropy energy of L1(0) CoPt-B thin films elongated c-axis Peer-reviewed

H Yamaguchi, O Kitakami, S Okamoto, Y Shimada, K Oikawa, K Fukamichi, TH Chiang

MATERIALS TRANSACTIONS　44　(8)　1514-1517　2003/08

DOI： 10.2320/matertrans.44.1514 　

ISSN： 1345-9678

eISSN： 1347-5320
Sensitive detection of irreversible switching in a single FePt nanosized dot Peer-reviewed

N. Kikuchi, S. Okamoto, O. Kitakami, Y. Shimada, K. Fukamichi

Applied Physics Letters　82　(24)　4313-4315　2003/06/16

DOI： 10.1063/1.1580994 　

ISSN： 0003-6951
Fabrication of two-dimensional assembly of L1(0), FePt particles Peer-reviewed

Y Shimada, T Sakurai, T Miyazaki, O Kitakami, S Okamoto

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS　262　(2)　329-338　2003/06

DOI： 10.1016/S0304-8853(02)01505-6 　

ISSN： 0304-8853
Fabrication of two-dimensional assembly of L10FePt nanoparticles Peer-reviewed

T. Miyazaki, S. Okamoto, O. Kitakami, Y. Shimada

Journal of Applied Physics　93　(10)　7759-7761　2003/05/15

DOI： 10.1063/1.1558053 　

ISSN： 0021-8979
Energy barrier enhanced by higher order magnetic anisotropy terms Peer-reviewed

O Kitakami, S Okamoto, N Kikuchi, Y Shimada

JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS　42　(5A)　L455-L457　2003/05

DOI： 10.1143/JJAP.42.L455 　

ISSN： 0021-4922
Brillouin light scattering from spin waves in epitaxial hcp Co films Peer-reviewed

A Yoshihara, J Mawatari, H Sato, S Okamoto, O Kitakami, Y Shimada

PHYSICAL REVIEW B　67　(13)　134435　2003/04

DOI： 10.1103/PhysRevB.67.134435 　

ISSN： 1098-0121
磁性体の熱揺らぎ評価 Peer-reviewed

岡本聡, 北上修, 指宿隆弘, 島田寛

日本金属学会報まてりあ　42　(6)　1047-1053　2003/04
Publisher: The Japan Institute of Metals and Materials
DOI： 10.2320/materia.42.475 　

ISSN： 1340-2625
Size dependences of magnetic properties and switching behavior in FePt (formula presented) nanoparticles Peer-reviewed

S. Okamoto, O. Kitakami, N. Kikuchi, T. Miyazaki, Y. Shimada, Y. K. Takahashi

Physical Review B - Condensed Matter and Materials Physics　67　(9)　2003/03/26

DOI： 10.1103/PhysRevB.67.094422 　

ISSN： 1550-235X 1098-0121
Size dependences of magnetic properties and switching behavior in FePt L10 nanoparticles

S. Okamoto, O. Kitakami, N. Kikuchi, T. Miyazaki, Y. Shimada, Y. K. Takahashi

Physical Review B - Condensed Matter and Materials Physics　67　(9)　944221-944227　2003/03/01

ISSN： 0163-1829
Size dependences of magnetic properties and switching behavior in FePt L1(0) nanoparticles Peer-reviewed

S Okamoto, O Kitakami, N Kikuchi, T Miyazaki, Y Shimada, YK Takahashi

PHYSICAL REVIEW B　67　(9)　94422　2003/03

DOI： 10.1103/PhysRevB.67.094422 　

ISSN： 2469-9950

eISSN： 2469-9969
Chemical-order-dependent magnetic anisotropy and exchange stiffness constant of FePt (001) epitaxial films Peer-reviewed

S. Okamoto, N. Kikuchi, O. Kitakami, T. Miyazaki, Y. Shimada, K. Fukamichi

Physical Review B - Condensed Matter and Materials Physics　66　(2)　244131-244139　2002/07/01
Publisher: American Physical Society
DOI： 10.1103/PhysRevB.66.024413 　

ISSN： 0163-1829
Chemical-order-dependent magnetic anisotropy and exchange stiffness constant of FePt (001) epitaxial films Peer-reviewed

S Okamoto, N Kikuchi, O Kitakami, T Miyazaki, Y Shimada, K Fukamichi

PHYSICAL REVIEW B　66　(2)　1-9　2002/07

DOI： 10.1103/PhysRevB.66.024413 　

ISSN： 1098-0121
Thermodynamic calculations of the effect of B and Ta on magnetically induced phase separation in Co-Cr-Pt alloys Peer-reviewed

K Oikawa, GW Qin, S Okamoto, O Kitakami, Y Shimada, K Fukamichi, K Ishida

APPLIED PHYSICS LETTERS　80　(15)　2704-2706　2002/04

DOI： 10.1063/1.1469684 　

ISSN： 0003-6951
Low-temperature formation of ordering phase in FePt films with Bi under layer Peer-reviewed

T. Miyazaki, S. Okamoto, O. Kitakami, Y. Shimada

Journal of the Magnetics Society of Japan　26　(4)　430-432　2002/04
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.26.430 　

ISSN： 0285-0192

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We investigated the L1₀ ordering process of FePt films deposited on a Bi underlayer. When annealed at relatively low temperatures, Bi tends to move toward the surface of an FePt layer. It was found that Bi travels along the grain boundary of FePt. This accelerates coalescence of FePt grains with intensive atomic diffusion, which leads to faster transformation from the disordered phase to the ordered. Subsequent rapid increase of coercivity is observed after annealing at 350°C. This appreciable reduction of ordering temperature may remove the difficulty of fabrication of L1₀-type, high-density recording media.
L1₀-FePt films with particulate structure Peer-reviewed

O. Kitakami, S. Okamoto, N. Kikuchi, T. Miyazaki, Y. Shimada

Journal of the Magnetics Society of Japan　26　1047-1053　2002/04
Trend of patterned media Peer-reviewed

S. Okamoto, N. Kikuchi, O. Kitakami, Y. Shimada

Material Stage　2　1-6　2002/04
Enhancement of magnetic anisotropy of hydrogenated Pd/Co/Pd trilayers Peer-reviewed

Satoshi Okamoto, Osamu Kitakami, Yutaka Shimada

Journal of Magnetism and Magnetic Materials　239　(1-3)　313-315　2002/02

DOI： 10.1016/S0304-8853(01)00596-0 　

ISSN： 0304-8853
Vertical bistable switching of spin vortex in a circular magnetic dot Peer-reviewed

N. Kikuchi, S. Okamoto, O. Kitakami, Y. Shimada, S. G. Kim, Y. Otani, K. Fukamichi

Journal of Applied Physics　90　(12)　6548-6549　2001/12/15

DOI： 10.1063/1.1416132 　

ISSN： 0021-8979
Effects of B and C on the ordering of L10-CoPt thin films Peer-reviewed

H. Yamaguchi, O. Kitakami, S. Okamoto, Y. Shimada, K. Oikawa, K. Fukamichi

Applied Physics Letters　79　(13)　2001-2003　2001/09/24

DOI： 10.1063/1.1408605 　

ISSN： 0003-6951
Magnetic characterization of Co-Pt particles produced by sputtering Peer-reviewed

T. Ibusuki, O. Kitakami, Y. Endo, S. Okamoto, Y. Shimada

Scripta Materialia　44　(8-9)　1327-1331　2001/05/18

DOI： 10.1016/S1359-6462(01)00703-5 　

ISSN： 1359-6462
Vertical Magnetization Process in Sub-micron Permalloy Disks Peer-reviewed

N. Kikuchi, S. Okamoto, O. Kitakami, Y. Shimada, S. G. Kim, Y. Otani, K. Fukamichi

IEEE Transactions on Magnetics　37　(4)　2082-2084　2001/04
Publisher: Institute of Electrical and Electronics Engineers
DOI： 10.1109/20.951060 　

ISSN： 0018-9464
Enhancement of Surface Anisotropy of Co/Pt, Pd Multilayers by Sm Addition Peer-reviewed

Satoshi Okamoto, Katsuya Nishiyama, Osamu Kitakami, Yutaka Shimada

Journal of Applied Physics　90　4085-4088　2001/04
Large Coercivity and Surface Anisotropy in MgO/Co Multilayer Films Peer-reviewed

Jian-Wang Cai, Satoshi Okamoto, Osamu Kitakami, Yutaka Shimada

Physical Review: Third series B, Condensed Matter and Materials Phyic　63　(104418)　1-8　2001/04
Magnetic Properties of Pd/Co/Pd Trilayers in Hydrogen Gas Atmsphere Peer-reviewed

S. Okamoto, K. Nishiyama, O. Kitakami, Y. Shimada

Journal of Magnetics Society of Japan　25　(4)　839-842　2001/04
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.25.839 　

ISSN： 0285-0192

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We studied the effect of hydrogenation on the magnetic properties of Pd/Co/Pd (111) trilayers. Hydrogen gas pressure P_H was varied from 1.3 to 3 atm. In this range of P_H, the Pd layer transformed to the β Pd-H phase. Induced magnetization at the interface of Co and Pd decreased in a hydrogen gas atmosphere, but its value did not reach zero. This means that the magnetic polarization of β Pd-H at the interface of Co remains. The perpendicular magnetic anisotropy is enhanced at P_H = 1.3 atm due to the large increase in magnetic surface anisotropy of Co. Sequential increase of P_H led to a monotonic decrease in magnetic anisotropy.
Magnetic Properties of Co/Pt Multilayer Dots Peer-reviewed

N. Kikuchi, S. Okamoto, O. Kitakami, Y. Shimada, S. G. Kim, Y. Otani, K. Fukamichi

Journal of Magnetics Society of Japan　25　(4)　859-862　2001/04
Publisher: The Magnetics Society of Japan
DOI： 10.3379/jmsjmag.25.859 　

ISSN： 0285-0192

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We fabricated submicron Co/Pt multilayer circular dot arrays using the electron beam lithography and the lift-off technique. Perpendicular anisotropy (K₁^eff) of these dot arrays was controlled in the range of 6.0 to -2.0 × 10⁶ erg/cc. We then investigated domain structures and switching processes of these dots using MFM and PMOKE. The domain structures of the dot array with K₁^eff = 6.0 × 10⁶ erg/cc ( t_Co = 0.5 nm) change from multi-domain to single-domain state as decreasing dot diameter to the domain size. The single-domain dots can take only two stable states (spin-up or -down) during the magnetization process, indicating that domain size in the continuous film is a key factor for designing bi-stable memory arrays and, moreover, that Co/Pt dots are good candidates as patterned memory elements.
Determination of first and second magnetic anisotropy constants of magnetic recording media Peer-reviewed

Yasushi Endo, Osamu Kitakami, Satoshi Okamoto, Yutaka Shimada

Applied Physics Letters　77　(11)　1689-1691　2000/09/11
Publisher: American Institute of Physics Inc.
DOI： 10.1063/1.1310166 　

ISSN： 0003-6951
Ordering and orientation of CoPt/SiO2 granular films with additive Ag Peer-reviewed

C Chen, O Kitakami, S Okamoto, Y Shimada

APPLIED PHYSICS LETTERS　76　(22)　3218-3220　2000/05

ISSN： 0003-6951
Long-range atomic ordering and magnetic properties of Co1-xPtx/SiO2 granular films Peer-reviewed

C Chen, O Kitakami, S Okamoto, Y Shimada

JOURNAL OF APPLIED PHYSICS　87　(9)　6947-6949　2000/05

ISSN： 0021-8979
Crystal distortion and the magnetic moment of epitaxially grown α″-Fe16N2 Peer-reviewed

Satoshi Okamoto, Osamu Kitakami, Yutaka Shimada

Journal of Magnetism and Magnetic Materials　208　(1)　102-114　2000
Publisher: Elsevier Science Publishers B.V.
DOI： 10.1016/S0304-8853(99)00556-9 　

ISSN： 0304-8853
Surface anisotropy in giant magnetic coercivity effect of cubic granular FeCo/SiO2 and NiCo/SiO2 films: A comparison with Neel's theory Peer-reviewed

C Chen, O Kitakami, S Okamoto, Y Shimada

JOURNAL OF APPLIED PHYSICS　86　(4)　2161-2165　1999/08

ISSN： 0021-8979
Effect of lattice distortion on magnetic and electronic state of alpha ''-Fe16N2 Peer-reviewed

S Okamoto, O Kitakami, Y Shimada

JOURNAL OF APPLIED PHYSICS　85　(8)　4952-4954　1999/04

ISSN： 0021-8979
Magnetocrystalline anisotropy of binary and ternary Co-Cr-X (X=Ta, Pt) alloys

O. Kitakami, N. Kikuchi, S. Okamoto, Y. Shimada, K. Oikawa, Y. Otani, K. Fukamichi

Digests of the Intermag Conference　1999
Publisher: IEEE
ISSN： 0074-6843
Magnetic surface anisotropy of fcc-Co-few(111)/Pd multilayers

S. Okamoto, O. Kitakami, Y. Shimada

Digests of the Intermag Conference　1999
Publisher: IEEE
ISSN： 0074-6843
Magnetic anisotropy of Co-5d transition metal alloys

N. Kikuchi, O. Kitakami, S. Okamoto, Y. Shimada, A. Sakuma, Y. Otani, K. Fukamichi

Digests of the Intermag Conference　1999
Publisher: IEEE
ISSN： 0074-6843
Very large coercivity and granular structure of CoPt/SiO2 films

Chen Chen, Osamu Kitakami, Satoshi Okamoto, Yutaka Shimada

Digests of the Intermag Conference　1999
Publisher: IEEE
ISSN： 0074-6843
Effects of Pt and Ta on the magnetic anisotropy of Co and Co-Cr thin films Peer-reviewed

Osamu Kitakami, Nobuaki Kikuchi, Satoshi Okamoto, Yutaka Shimada, Katsunari Oikawa, Yoshichika Otani, Kazuaki Fukamichi

Journal of Magnetism and Magnetic Materials　202　(2)　305-310　1999
Publisher: Elsevier Science Publishers B.V.
DOI： 10.1016/S0304-8853(99)00368-6 　

ISSN： 0304-8853
Magnetic surface anisotropy of fcc-Co-Fe (111) / Pd multilayers Peer-reviewed

Satoshi Okamoto, Osamu Kitakami, Yutaka Shimada

IEEE Transactions on Magnetics　35　(5)　3031-3033　1999

DOI： 10.1109/20.801075 　

ISSN： 0018-9464
Ferromagnetic resonance in epitaxial alpha'-martensite Fe-N films Peer-reviewed

O Kohmoto, S Okamoto, O Kitakami, Y Shimada, T Tsuda

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS　36　(7A)　4305-4306　1997/07

ISSN： 0021-4922
Growth of Thin Films by Sputter Beam Method.

Shimada Yutaka, Okamoto Satoshi, Kitakami Osamu

Bulletin of the Japan Institute of Metals　36　(10)　1016-1020　1997
Publisher: The Japan Institute of Metals and Materials
DOI： 10.2320/materia.36.1016 　

ISSN： 1340-2625
Crystal structure and magnetic properties of Fe (111) singe crystal films Peer-reviewed

Y. Endo, S. Okamoto, O. Kitakami, Y. Shimada

Journal of Applied Physics　81　(1)　344-349　1997/01/01
Publisher: American Institute of Physics Inc.
DOI： 10.1063/1.364117 　

ISSN： 0021-8979
Effect of surface free energy of underlayer materials on crystal growth of Co polycrystalline films Peer-reviewed

O. Kitakami, S. Okamoto, Y. Shimada

Journal of Applied Physics　79　(9)　6880-6883　1996/05/01
Publisher: American Institute of Physics Inc.
DOI： 10.1063/1.361510 　

ISSN： 0021-8979
alpha''-Fe16N2 phase epitaxially grown by sputter beam method Peer-reviewed

S Okamoto, O Kitakami, Y Shimada

JOURNAL OF APPLIED PHYSICS　79　(8)　5250-5252　1996/04

ISSN： 0021-8979
#Galpha#GR-Fe₁₆N₂ phase epitaxially grown of Fe and Ag underlayers Peer-reviewed

岡本聡

Jonrnal of Applied Physics　79　(8)　5250　1996/04

DOI： 10.1063/1.361301 　
Characterization of epitaxially Fe-N films grown by Sputter-Beam method Peer-reviewed

岡本聡

Journal of Applied Physics　79　(3)　1678-1683　1996/04
Publisher: American Institute of Physics
DOI： 10.1063/1.361421 　

ISSN： 0021-8979
Improvement in magnetoresistance of very thin permalloy films by post-annealing Peer-reviewed

Hiroshi Funaki, Satoshi Okamoto, Osamu Kitakami, Yutaka Shimada

Japanese Journal of Applied Physics　33　(9)　L1304-L1306　1994

DOI： 10.1143/JJAP.33.L1304 　

ISSN： 1347-4065 0021-4922
Properties of Fe(001) single-crystal films grown by sputter beam method Peer-reviewed

Satoshi Okamoto, Osamu Kitakami, Yutaka Shimada

Japanese Journal of Applied Physics　33　(11R)　616-617　1994

DOI： 10.1143/JJAP.33.6164 　

ISSN： 1347-4065 0021-4922
Fe-Single-Crystal films prepared by the Sputter-Beam Method Peer-reviewed

岡本聡

Journal of the Magnetic Society of Japan　17　(2)　307-310　1993/04

DOI： 10.3379/jmsjmag.17.307 　
Crystal structure and magnetoresistance of fe10ni90 films deposited by sputter-beam method Peer-reviewed

Yukimasa Yokoyama, Satoshi Okamoto, Osamu Kitakami, Yutaka Shimada, Fuminori Watanabe, Shinji Kondo, Atsushi Hayashi, Hiroyuki Fujita

Japanese Journal of Applied Physics　32　(9)　L1222-L1224　1993

DOI： 10.1143/JJAP.32.L1222 　

ISSN： 1347-4065 0021-4922

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Misc. 118

軟磁性材料の高周波損失に関する研究の現状と課題 Invited

岡本聡, 小野暢久, 谷口卓也, 塚原宙, 鈴木清策

固体物理　60　299-308　2025/06
軟磁性圧粉コアの高精度鉄損測定と鉄損解析 Invited Peer-reviewed

岡本聡, 小野暢久, 谷口卓也, 佐藤佑樹, 上原裕二

日本磁気学会誌まぐね　19　207-211　2024/11
Time-varying Permeability Metamaterials towards Microwave Frequency Conversion

児玉俊之, 菊池伸明, 岡本聡, 岡本聡, 大野誠吾, 冨田知志, 冨田知志

日本磁気学会学術講演概要集　48th　2024

ISSN： 1882-2959
Nd-Fe-B熱間加工磁石の3次元磁化反転過程解析に向けた磁区抽出

諏訪智巳, 鈴木基寛, 大久保忠勝, 入山恭彦, 宮脇寛, 谷口卓也, 岡本聡

日本金属学会講演大会(Web)　175th　2024
Evaluation of Spin-Current-Induced Permeability Variation toward Time-Varying Magnetic Metamaterials

児玉俊之, 菊池伸明, 岡本聡, 岡本聡, 大野誠吾, 冨田知志, 冨田知志

日本磁気学会論文特集号(Web)　8　(1)　2024

ISSN： 2432-0471
Tb拡散Nd-Fe-B焼結磁石の 3次元微細組織と磁区構造からの特徴抽出

諏訪智巳, 石上啓介, 岡本聡, 鈴木基寛

電気学会マグネティクス研究会資料　MAG-23　074　2023/08
マイクロ波アシスト磁化反転と熱揺らぎ

菊池伸明, 佐藤勝成, 水谷聡志, 畑山正寿, 島津武仁, 岡本聡

信学技報　37-42　2023/06
Permeability Control of Co Wires by Spin-current Injection for Time-varying Metamaterials

清水蓮也, 児玉俊之, 菊池伸明, 岡本聡, 岡本聡, 大野誠吾, 冨田知志, 冨田知志

応用物理学会春季学術講演会講演予稿集(CD-ROM)　70th　2023

ISSN： 2758-4704
時間変調メタマテリアルに向けたスピン流誘起透磁率制御

児玉俊之, 菊池伸明, 岡本聡, 岡本聡, 大野誠吾, 冨田知志, 冨田知志

電子情報通信学会技術研究報告(Web)　123　(65(MRIS2023 1-7))　2023

ISSN： 2432-6380
Spin-current Induced Permeability Control of NiFe Wires towards Time-varying Metamaterials

児玉俊之, 菊池伸明, 岡本聡, 岡本聡, 大野誠吾, 冨田知志, 冨田知志

応用物理学会春季学術講演会講演予稿集(CD-ROM)　70th　2023

ISSN： 2436-7613
放射光X線磁気トモグラフィーによる永久磁石材料内部の3次元磁区構造観察 Invited

鈴木基寛, 岡本聡

まぐね　17　187-193　2022/07
極薄化によSm(Fe₈₀CO₂₀)₁₂微粒子薄膜の作製と保磁力発現可能性の検討 (マグネティックス研究会ナノスケール構造磁性体、永久磁石、磁性材料、磁気応用一般)

芳賀僚太, 菊池伸明, 岡本聡, 高橋有紀子

電気学会研究会資料. MAG = The papers of technical meeting on magnetics, IEE Japan　2021　(82)　37-40　2021/08/06
Publisher: 電気学会
初等連載講座磁性材料と電磁波第3回マイクロ波帯での磁化ダイナミクス Invited Peer-reviewed

岡本聡

日本磁気学会誌まぐね　16　(4)　202-208　2021/08
Effect of thermal fluctuations on microwave assisted switching in Co/Pt nanodot array

45　(14)　7-11　2021/06
Publisher: 映像情報メディア学会
ISSN： 1342-6893
Analysis on thermally activated magnetization reversal of permanent magnets Invited

Satoshi Okamoto

Magnetics Japan　16　(1)　38-43　2021/02
Three-dimensional observation of magnetic domain in fine-grained Nd-Fe-B sintered magnet by hard X-ray magnetic tomography

竹内誠, 芳賀僚太, 菊池伸明, 岡本聡, 鈴木基寛, 小林慎太郎, 中村哲也, 中村哲也, 大久保忠勝, 埋橋淳, 宇根康裕

電気学会研究会資料　MAG-20　(MAG-20-108-115)　113　2020/12
マイクロ波アシスト磁化反転 Invited

菊池伸明, 岡本聡, 北上修, 島津武仁

日本磁気学会誌まぐね　15　89　2020/04
トランス結合型透磁率測定装置

田丸慎吾, 菊池伸明, 五十嵐利行, 岡本聡, 久保田均, 吉田栄吉

日本磁気学会誌まぐね　15　134　2020/04
Effects of inter-grain exchange coupling on microwave assisted magnetization switching on CoCrPt granular thin films

2019　(197)　13-17　2019/12/19
Publisher: 電気学会
W下地を用いたSm(Fe,Ti)₁₂エピタキシャル微粒子薄膜の作製 (マグネティックス研究会ナノスケール構造磁性体,磁性材料,磁気応用一般)

近藤司, 岡本聡, 菊池伸明, 芳賀僚太, 北上修

電気学会研究会資料. MAG = The papers of technical meeting on magnetics, IEE Japan　2019　(197)　51-56　2019/12/19
Publisher: 電気学会
Study on magnetization reversal process of hot-deformed Nd-Fe-B magnets using soft X-ray magnetic circular dichroism microscopy

2019　(79)　51-55　2019/08/08
Publisher: 電気学会
Microwave assisted magnetization switching experiments on CoCrPt granular media

119　(79)　9-14　2019/06/13
Publisher: 電子情報通信学会
ISSN： 0913-5685
Microwave assisted magnetization switching experiments on CoCrPt granular media

43　(15)　9-14　2019/06
Publisher: 映像情報メディア学会
ISSN： 1342-6893
マイクロ波アシスト磁気記録における磁化反転挙動 (磁気記録・情報ストレージ)

岡本聡, 菊池伸明, 北上修, 島津武仁

電子情報通信学会技術研究報告 = IEICE technical report : 信学技報　118　(490)　33-36　2019/03/08
Publisher: 電子情報通信学会
ISSN： 0913-5685
マイクロ波アシスト磁気記録における磁化反転機構 (マグネティックス電子材料合同研究会光記録・磁気記録・一般)

岡本聡, 菊池伸明, 北上修, 島津武仁

電気学会研究会資料. EFM　2019　(1)　33-36　2019/03/08
Publisher: 電気学会
マイクロ波アシスト磁気記録における磁化反転機構 (マグネティックス電子材料合同研究会光記録・磁気記録・一般)

岡本聡, 菊池伸明, 北上修, 島津武仁

電気学会研究会資料. MAG = The papers of technical meeting on magnetics, IEE Japan　2019　(14)　33-36　2019/03/08
Publisher: 電気学会
FORC analysis on Nd-Fe-B sintered magnets

宮澤和則, 岡本聡, 蓬田貴裕, 菊池伸明, 北上修

電気学会研究会資料. MAG = The papers of technical meeting on magnetics, IEE Japan　2018　(184)　35-40　2018/12/11
Publisher: 電気学会
Magnetics and Optics Research FOREWORD

Hiro Munekata, Timothy Benseman, Taichi Goto, Iwao Matsuda, Satoshi Okamoto, Koji Sekiguchi, Yu Shiratsuchi

JAPANESE JOURNAL OF APPLIED PHYSICS　57　(9)　2018/09

DOI： 10.7567/JJAP.57.09T001 　

ISSN： 0021-4922

eISSN： 1347-4065
Ultra-high sensitive magnetization measurement for a very small area of Nd-Fe-B hot-deformed magnet using anomalous Hall effect

蓬田貴裕, 岡本聡, 菊池伸明, 北上修, Sepehri-Amin H, 大久保忠勝, 宝野和博, 秋屋貴博, 服部篤, 日置敬子

電気学会研究会資料. MAG = The papers of technical meeting on magnetics, IEE Japan　2018　(81)　65-69　2018/08/09
Publisher: 電気学会
First-order reversal curve (FORC)解析と永久磁石材料への適用

岡本聡, 蓬田貴裕, 宮澤和則, 菊池伸明, 北上修, 渡辺奈生巳, 吹田尚久

まてりあ　53　(9)　533-540　2017/09
Publisher: The Japan Institute of Metals and Materials
DOI： 10.2320/materia.56.533 　

ISSN： 1340-2625

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1521
Magnetization switching behavior in single epitaxial Co/Pt multilayer dot (磁気記録・情報ストレージ)

Lao Bin, Okamoto Satoshi, Kikuchi Nobuaki, Kitakami Osamu

電子情報通信学会技術研究報告 = IEICE technical report : 信学技報　116　(83)　17-20　2016/06/09
Publisher: 電子情報通信学会
ISSN： 0913-5685
Magnetization switching behavior in single epitaxial Co/Pt multilayer dot (マルチメディアストレージ)

Lao Bin, Okamoto Satoshi, Kikuchi Nobuaki, Kitakami Osamu

映像情報メディア学会技術報告 = ITE technical report　40　(16)　17-20　2016/06
Publisher: 映像情報メディア学会
ISSN： 1342-6893
22aBP-10 Coplanar-waveguide ferromagnetic resonance of a single magneto-chiral metamolecule

Kodama T, Kusanagi Y, Okamoto S, Kikuchi N, Kitakami O, Tomita S, Hosoito N, Yanagi H

Meeting Abstracts of the Physical Society of Japan　71　(0)　2016
Publisher: 一般社団法人日本物理学会
A Theoretical Study of Thermally Activated Magnetization Switching under Microwave Assistance Peer-reviewed

H. Suto, K. Kudo, T. Nagasawa, T. Kanao, K. Mizushima, R. Sato, S. Okamoto, N. Kikuchi, O. Kitakami, T. Shimatsu

2015 IEEE MAGNETICS CONFERENCE (INTERMAG)　2015
Magnetization switching dynamics in single nanodot of epitaxial Co/Pt multilayer. Peer-reviewed

B. Lao, S. Okamoto, N. Kikuchi, O. Kitakami

2015 IEEE MAGNETICS CONFERENCE (INTERMAG)　2015
ナノ磁性体における磁化反転ダイナミクスとその応用

岡本聡

日本磁気学会誌まぐね　9　(2)　76-83　2014/02
Publisher: 日本応用磁気学会
ISSN： 1880-7208
Microwave Assisted Magnetization Switching in Perpendicular Magnetic Nanoelements

Okamoto Satoshi

IEICE technical report. Component parts and materials　113　(231)　17-20　2013/10/08
Publisher: The Institute of Electronics, Information and Communication Engineers
ISSN： 0913-5685

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Magnetic recording has been a key role as a infrastructure for the present information technology. The physical limitation of recording density for the present recording system, however, has been very serious due to the so-called trilemma problem. Microwave assisted magnetization switching which is newly proposed as one of the future recording technologies has been expected to overcome the trilemma problem. We have investigated the theoretical treatments and the fundamental experiments using nanostructured perpendicular magnetic elements. For the magnetic dot size〜50 nm, the switching behaviors can be well explained by the simple analytical model under the rotating frame. On the other hand, for the dot size>100 nm, it is observed that the assistance effect significantly is enhanced. This very enhanced assistance effect is also well explained by the spin wave excitation in the dot. Thus, it is concluded that the microwave assisted switching is well described by the simple theories, and these simple behaviors would be useful for the design of future recording system.
Analytical study experimental verifications on microwave assisted magnetization switching

岡本聡, 古田正樹, 菊池伸明

映像情報メディア学会技術報告 = ITE technical report　37　(26)　33-38　2013/06
Publisher: 映像情報メディア学会
ISSN： 1342-6893
Perpendicular magnetic anisotropy and time-resolved magnetization dynamics of Co/Ni multilayers

KATO Takeshi, MATSUMOTO Yoshihiro, IWATA Satoshi, OKAMOTO Satoshi, KIKUCHI Nobuaki, KITAKAMI Osamu, TSUNASHIMA Shigeru

2011　(91)　109-114　2011/11/24
単一磁性ナノ粒子の振舞い

北上修, 岡本聡, 菊池伸明

マテリアルインテグレーション　24　(4,5)　71-76　2011/05
Magnetic properties and behavior of nanomagnets: toward development of ultra high density magnetic memory

Materials integration　24　(4)　71-76　2011/04
Publisher: ティー・アイ・シィー
ISSN： 1344-7858
Microwave assisted magnetization switching and its switching mechanism

OKAMOTO S, KIKUCHI N, KITAKAMI O

日本磁気学会研究会資料 = Bulletin of Topical Symposium of the Magnetics Society of Japan　177　39-44　2011/03/18
Publisher: 日本磁気学会
ISSN： 1882-2940
マイクロ波アシスト記録における磁化反転条件とそのダイナミクス

岡本聡, 菊池伸明, 北上修

電子情報通信学会技術研究報告. MR, 磁気記録　110　(310)　7-11　2010/11/19
Publisher: 一般社団法人電子情報通信学会
ISSN： 0913-5685
マイクロ波アシスト記録における磁化反転条件とそのダイナミクス (マルチメディアストレージ)

岡本聡, 菊池伸明, 北上修

映像情報メディア学会技術報告　34　(50)　7-11　2010/11
Publisher: 映像情報メディア学会
ISSN： 1342-6893
Nano-dot array fabrication by using AFM nano-indentation technique

HASHIMOTO Tomohiko, OKAMOTO Satoshi, KIKUCHI Nobuaki, KITAKAMI Osamu

電気学会研究会資料. MAG, マグネティックス研究会　2009　(168)　31-34　2009/12/01
Magnetic behavior of recording materials in nanoscale regime

KITAKAMI O., OKAMOTO S., KIKUCHI N., SHIMATSU T., SATO H., MITSUZUKA K., AOI H.

Bulletin of Topical Symposium of the Magnetics Society of Japan　165　31-38　2009/03/13
Publisher: 日本磁気学会
ISSN： 1882-2940
CS-8-4 Switching condition and its dynamics for microwave assisted magnetization switching

Okamoto Satoshi, Kikuchi Nobuaki, Kitakami Osamu

Proceedings of the IEICE General Conference　2009　(2)　"S-65"-"S-66"　2009/03/04
Publisher: 一般社団法人電子情報通信学会
Intrinsic permeability of fine particles and effect of composite particle structure

SHIMADA Y., ENDO Y., YAMAGUCHI M., OKAMOTO S., KITAKAMI O.

2008　(191)　49-52　2008/12/18
スパッタリング法によるL11型Co-Pt規則化合金膜の作製とその磁気特性

島津武仁, 佐藤英夫, 青井基, 村岡裕明, 岡本聡, 北上修

日本磁気学会誌まぐね　2008
ナノ磁性体と高密度スピントロニクスデバイス

北上修, 岡本聡, 菊池伸明

未来材料　8　(3)　30-36　2008
Publisher: エヌ・ティー・エス
ISSN： 1346-0986
Synethesis of submicron particles and application to RF materials

SHIMADA Yutaka, YAMAGUTI Masahir, OKAMOTO Satoshi, KITAKAMI Osamu

2007　(42)　7-10　2007/07/12
Detection of magnetization reversal of single Co/Pt dot

KATO T, KIKUCHI N, OKAMOTO S, KITAKAMI O, TEZUKA N, SUGIMOTO S

電気学会研究会資料. MC, 金属・セラミックス研究会　2006　(1)　5-9　2006/11/28
Ni₄₃Co₇Mn₃₉Sn₁₁ホイスラー合金のメタ磁性形状記憶効果

及川勝成, 今野陽介, 伊東航, 森戸春彦, 須藤祐司, 岡本聡, 北上修, 藤田麻哉, 貝沼亮介, 鹿又武, 石田清仁

日本金属学会講演概要　139th　295　2006/09/16

ISSN： 1342-5730
Prototype fabrication of fast pulse field generator

ITO Atsuo, KIKUCHI Nobuaki, OKAMOTO Satoshi, KITAKAMI Osamu, SHIMADA Yutaka

電気学会研究会資料. MAG, マグネティックス研究会　2006　(98)　13-18　2006/08/04
高密度記録材料

北上修, 岡本聡, 菊池伸明

月間オプトロニクス　296　104-110　2006/04
Ni‐Mn‐In‐Co合金におけるメタ磁性形状記憶効果

貝沼亮介, 今野陽介, 伊東航, 須藤祐司, 森戸晴彦, 岡本聡, 北上修, 及川勝成, 藤田麻哉, 鹿又武, 石田清仁

日本金属学会講演概要　138th　239　2006/03/21

ISSN： 1342-5730
Ni₄₆Mn₄₁In₁₃合金のマルテンサイト変態に及ぼす磁場の効果

及川勝成, 今野陽介, 伊東航, 須藤裕司, 森戸晴彦, 岡本聡, 北上修, 貝沼亮介, 藤田麻哉, 鹿又武, 石田清仁

日本金属学会講演概要　138th　239　2006/03/21

ISSN： 1342-5730
L1_0 FePt, CoPt alloys for future high density recording

KITAKAMI O, OKAMOTO S, KIKUCHI N

日本応用磁気学会研究会資料　146　53-58　2006/02/20

ISSN： 1340-7562
Structural and Magnetic Properties of FePt-5%B thin Film by Post-Annealing

LEE Young-min, LEE Byeong-Seon, LEE Chan-Gyu, KOO Bon-Heun, SHIMADA Y., KITAKAMI O., OKAMOTO S., MIYAZAKI T.

2005　(124)　163-166　2005/12/05
FMR study on spin-sprayed Ni-Zn-Co ferrite films with. high permeability usable for GHz noise suppressors

K Kondo, T Chiba, S Yoshida, S Okamoto, Y Shimada, N Matsushita, M Abe

IEEE TRANSACTIONS ON MAGNETICS　41　(10)　3463-3465　2005/10

DOI： 10.1109/TMAG.2005.854884 　

ISSN： 0018-9464
Magnetization reversal process of L1_0-FePt nanoparticle

OKAMOTO S., MIYAZAKI T., KITAKAMI O., SHIMADA Y.

2005　(12)　37-41　2005/03/11
超高密度記録材料としてのL10-FePt

岡本聡, 宮崎孝道, 北上修, 島田寛

日本応用磁気学会第139回研究会資料「超高密度記録の更なる飛躍を目指して」　139　95-104　2005/02

ISSN： 1340-7562
Effects of Additives on L1_0 Ordering and Magnetic Properties of Co-Pt Films

KITAKAMI O., YAMAGUCHI H., OKAMOTO S., SHIMADA Y.

28　582-583　2004/09/21
Attempt of magnetic nanodot array fabrication by Ar ion beam etching

OKAMOTO S., KITAKAMI O., SHIMADA Y.

28　128-128　2004/09/21
FMR study of plated Ni-Zn-Co ferrite films

KONDO Koichi, CHIBA Tatsuya, YOSHIDA Shigeyoshi, OKAMOTO Satoshi, SHIMADA Yutaka, MATSUSHITA Nobuhiro, ABE Masanori

28　479-479　2004/09/21
Size dependence of L1_0 ordering in FePt nanoparticles

MIYAZAKI T., TAKAHASHI Y. K., HONO K., MURAKAMI Y., SHINDO D., OKAMOTO S., KITAKAMI O., SHIMADA Y.

28　51-51　2004/09/21
K_<u2> effect in CoPtCr-SiO_2 perpendicular recording media : Magnetic anisotropy

SATO H., SHIMATSU T., MITSUZUKA K., KITAKAMI O., OKAMOTO S., MURAOKA H., AOI H., NAKAMURA Y.

28　163-163　2004/09/21
Preferential c-axis orientation of Co-Pt films on Ru and Pt underlayers

SAKURAI T., SHIBATA K., ISHIKAWA S., OKAMOTO S., KITAKAMI O., SHIMADA Y.

28　17-17　2004/09/21
Magnetization reversal of a single L1_0-FePt nanodot at low temperatures

TAKEUCHI H, ONO T, NASU S, KIKUCHI N, OKAMOTO S, KITAKAMI O, SHIMADA Y

日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan　28　152-152　2004/09/21
ナノ磁性粒子の磁化反転機構

岡本聡, 菊池伸明, 北上修, 島田寛

日本金属学会報まてりあ　43　737-743　2004/04

DOI： 10.2320/materia.43.737 　
Magnetic Anisotropy and Phase Separation of Co-Mo and Co-W Films

佐藤公宣, QIN G W, 及川勝成, 岡本聡, 北上修, 島田寛

日本応用磁気学会誌　28　(3)　2004

ISSN： 0285-0192
27aPS-56 Magnetization reversal of a single Ll_o-FePt nanodot at low temperatures

Takeuchi H, Ono T, Nasu S, Kikuchi N, Okamoto S, Kitakami O, Shimada Y

Meeting Abstracts of the Physical Society of Japan　59　(0)　448-448　2004
Publisher: The Physical Society of Japan
ISSN： 1342-8349
Phase separation of Co-Mo and Co-W films

SATO M., QIN G. W., OIKAWA K., OKAMOTO S., KITAKAMI O., SHIMADA Y.

27　211-211　2003/09/01

ISSN： 1340-8100
Study in c-axis orientation of L1_0-FePt films

FUJI Y., MIYAZAKI T., OKAMOTO S., KITAKAMI O., SHIMADA Y., KOIKE J.

27　237-237　2003/09/01

ISSN： 1340-8100
Fabrication of self-assembled FePt L1_0 (001) nanoparticles grown on MgO facetted structure

OKAMOTO S., KITAKAMI O., SHIMADA Y., TAKAHASHI Y., HONO K.

27　245-245　2003/09/01

ISSN： 1340-8100
Growth of L1_0 FePt(001) on c-axis oriented ZnO underlayers

SAKURAI T., IGARI Y., OKAMOTO S., KITAKAMI O., SHIMADA Y.

27　236-236　2003/09/01

ISSN： 1340-8100
Brillouin light scattering from spin waves in hcp epitaxial Co thin films

YOSHIHARA A., MAWATARI J-I., SATO H., OKAMOTO S., KITAKAMI O., SHIMADA Y.

27　451-451　2003/09/01

ISSN： 1340-8100
K_<u2> effect in CoPtCr-SiO_2/Ru perpendicular recording media

SHIMATSU T., OIKAWA T., KITAKAMI O., OKAMOTO S., MURAOKA H., AOI H., NAKAMURA Y.

27　526-526　2003/09/01

ISSN： 1340-8100
High perpendicular magnetic anisotropy in CoPtCr(-SiO_2)/Ru perpendicular films

SHIMATSU T., SATO H., OIKAWA T., INABA Y., KITAKAMI O., OKAMOTO S., MURAOKA H., AOI H., NAKAMURA Y.

27　527-527　2003/09/01

ISSN： 1340-8100
Magnetization reversals and thermal stability of fine particles for magnetic recording

KITAKAMI O, OKAMOTO S, KIKUCHI N, SHIMADA Y

日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan　27　164-165　2003/09/01

ISSN： 1340-8100
磁性体の熱揺らぎ評価

岡本聡, 北上修, 指宿隆弘, 島田寛

日本金属学会報まてりあ　42　1047-1053　2003/04

DOI： 10.2320/materia.42.475 　
Magnetization reversal of a single Ll_0-FePt nanodot at low temperatures

Takeuchi H, Ono T, Nasu S, Kikuchi N, Okamoto S, Kitakami O, Shimada Y

Meeting Abstracts of the Physical Society of Japan　58　(0)　373-373　2003
Publisher: The Physical Society of Japan
ISSN： 1342-8349
磁気記録媒体の基礎解析 [招待]

北上修, 岡本聡, 島田寛

日本応用磁気学会第128回研究会資料　128　(12)　93-103　2003/01
Bistable Magnetization Process of Submicron Ferromagnets

SHIMADA Yutaka, KIKUCHI N., OKAMOTO S., KITAKAMI O.

26　251-252　2002/09/01

ISSN： 1340-8100
Process of crystal orientation and ordering in epitaxial Fe/Pt multilayer films

MIYAZAKI T., FUJI Y., OKAMOTO S., KITAKAMI O, SHIMADA Y.

26　306-306　2002/09/01

ISSN： 1340-8100
Magnetic hardness and magnetization reversal process of FePt L1_0 (001) island particles

OKAMOTO S., KITAKAMI O., SHIMADA Y.

26　304-304　2002/09/01

ISSN： 1340-8100
Magnetization Measurements of Single FePt Dot by Extraordinary Hall Effects

KIKUCHI N, OKAMOTO S, KITAKAMI O, SHIMADA Y, FUKAMICHI K

日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan　26　47-47　2002/09/01

ISSN： 1340-8100
L1₀-FePt films with particulate structure

O. Kitakami, S. Okamoto, N. Kikuchi, T. Miyazaki, Y. Shimada

Journal of the Magnetics Society of Japan　26　1047-1053　2002/04
Trend of patterned media

S. Okamoto, N. Kikuchi, O. Kitakami, Y. Shimada

Material Stage　2　1-6　2002/04
Low temperature formation of ordering phase in FePt film with Bi under layer

MIYAZAKI T., OKAMOTO S., KITAKAMI O., SHIMADA Y.

25　157-157　2001/09/01

ISSN： 1340-8100
Evaluation of magnetic anisotropy for fine particles by AC susceptibility measurement

IBUSUKI T., SAKURAI T., OKAMOTO S., KITAKAMI O., SHIMADA Y.

25　163-163　2001/09/01

ISSN： 1340-8100
Characterization of magnetized orientation for magnets by using magneto-optic effect

OKAMOTO S., KOMURO M., SHIMADA Y.

25　438-438　2001/09/01

ISSN： 1340-8100
Magnetic properties at the interface of oxide/Fe multilayers

ENDO Yasushi, TAGUCHI Jun, OKAMOTO Satoshi, KITAKAMI Osamu, SHIMADA Yutaka

25　417-417　2001/09/01

ISSN： 1340-8100
Response to "Comment on 'Determination of first and second magnetic anisotropy constants of magnetic recording media' " [Appl. Phys. Lett. 79, 1733 (2001)]

Y Endo, O Kitakami, S Okamoto, Y Shimada

APPLIED PHYSICS LETTERS　79　(11)　1734-1734　2001/09

ISSN： 0003-6951
Evaluation of the wall energy of epitaxial FePt L1_0 (001) films

OKAMOTO S, KIKUCHI N, KITAKAMI O, SHIMADA Y

日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan　25　99-99　2001/09/01

ISSN： 1340-8100
Vertical magnetization switching of spin-vortex

KIKUCHI N, OKAMOTO S, KITAKAMI O, SHIMADA Y, KIM S. G, OTANI Y, FUKAMICHI K

日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan　25　255-255　2001/09/01

ISSN： 1340-8100
Bi-stable switching of micromagnetic structure

KIKUCHI N, OKAMOTO S, KITAKAMI O, SHIMADA Y, KIM S. G, OTANI Y, FUKAMICHI K

日本応用磁気学会研究会資料　119　17-23　2001/03/06

ISSN： 1340-7562
In-situ measurement of magnetic surface anisotropy of Pd/Co/Pd trilayers in H_2 atmosphere

OKAMOTO S., NISHIYAMA K., KITAKAMI O., SHIMADA Y.

24　327-327　2000/09/01

ISSN： 1340-8100
Measurements of magnetic surface anisotropy of Co alloys

OKAMOTO Satoshi, NISHUYAMA Katsuya, KITAKAMI Osamu, SHIMADA Yutaka

2000　(9)　11-14　2000/02/07
Magnetic Hardness in MgO/Co Multilayer Films

CAI Jian-Wang, OKAMOTO Satoshi, KITAKAMI Osamu, SHIMADA Yutaka

2000　(9)　1-6　2000/02/07
Influence of 5d transition elements on the magnetocrystalline anisotropy of hcp-Co

N Kikuchi, O Kitakami, S Okamoto, Y Shimada, A Sakuma, Y Otani, K Fukamichi

JOURNAL OF PHYSICS-CONDENSED MATTER　11　(43)　L485-L490　1999/11

DOI： 10.1088/0953-8984/11/43/103 　

ISSN： 0953-8984
Surface magnetic ansiotropy of Co-(Fe, Ni)/Pd(111) multilayer films

OKAMOTO S., NISHIYAMA K., KITAKAMI O., SHIMADA Y.

23　7-7　1999/10/01
Large coercivity and granular structure of CoPt/SiO2 films

C Chen, O Kitakami, S Okamoto, Y Shimada, K Shibata, M Tanaka

IEEE TRANSACTIONS ON MAGNETICS　35　(5)　3466-3468　1999/09

DOI： 10.1109/20.800559 　

ISSN： 0018-9464
About electronic structure of α"-Fe_<16>N_2

OKAMOTO S., KITAKAMI Osamu, SHIMADA Yutaka

22　272-272　1998/09/01
Surface magnetic anisotropy of Ag/Fe/Ag(001)single crystal films

OKAMOTO S., KITAKAMI Osamu, SHIMADA Yutaka

22　190-190　1998/09/01
A few measurements and discussions on the fabrication process of metallic particles using an AFM

OZAWA Tetsuya, OKAMOTO Satoshi, KITAKAMI Osamu, SHIMADA Yutaka

1998　(13)　41-47　1998/02/03
Relationship between magnetism and lattice distortion of α''-Fe_<16>N_2

OKAMOTO S., KITAKAMI Osamu, SHIMADA Yutaka

21　238-238　1997/10/01
FMR studies of epitaxial α'-martensite Fe-N films

KOHMOTO O., OKAMOTO S., KITAKAMI O., SHIMADA S., TSUDA T.

21　235-235　1997/10/01
Structural changes of α''-Fe_<16>N_2 on films thickness

OKAMOTO S., KITAKAMI Osamu, SHMADA Yutaka

21　237-237　1997/10/01
6a-PS-122 Magnetic Properties and Magnetoresistance of Submicron Fe Ferromagnetic Wires

Otani Y., Kim G., Fukamichi K., Okamoto S., Kitakami O., Shimada Y.

Meeting abstracts of the Physical Society of Japan　52　(2)　505-505　1997/09/16
Publisher: The Physical Society of Japan (JPS)
ISSN： 1342-8349
29p-WB-5 Magnetic Properties and Magnetoresistance of Submicron Ferromagnetic Wires

Otani Y., Fukamichi K., Okamoto S., Kitakami O., Shimada Y., Pannetier B., Matsuda T., Tonomura A.

Meeting abstracts of the Physical Society of Japan　52　(1)　483-483　1997/03/17
Publisher: The Physical Society of Japan (JPS)
ISSN： 1342-8349
Magnetic Properties and Magnetoresistance of Submicron Fe Ferromagnetic Wires

Otani Y., Fukamichi K., Okamoto S., Kitagami O., Shimada Y., Pannetier B.

Abstracts of the meeting of the Physical Society of Japan. Sectional meeting　1996　(3)　39-39　1996/09/13
Publisher: The Physical Society of Japan (JPS)
Properties changes of epitaxial Fe-N films on films thickness

OKAMOTO S., KITAKAMI Osamu, SHIMADA Yutaka

20　404-404　1996/09/01
The effect of structure changes on the magnetism of #Galpha#GR-Fe₁₆N₂

岡本聡

Bulletin of the Research Institute for Scientific Measurements. Tohoku University　45　(1)　33-46　1996/04
Publisher: 東北大学科学計測研究所
ISSN： 0040-8689
Crystal structure and Magnetic Property of Epitaxial Fe-N Films Grown by Sputter Beam Method

OKAMOTO S., KITAKAMI O., SHIMADA Y.

19　75-75　1995/09/01
Crystal structure and magnetic properties of Fe(111)single crystal film grown by the Sputter beam method

ENDO Y., OKAMOTO S., KITAKAMI O., SHIMADA Y.

19　183-a-183-b　1995/09/01
Thin film formation by Sputter Beam Method and the Magnetic properties

岡本聡

Bulletin of the Research Institute for Scientific Measurements, Tohoku University　44　(1)　27　1995/04
スパッタビーム法によるFe膜の結晶構造と磁気特性

岡本聡, 島田寛, 鈴木光政

日本応用磁気学会誌　17　(1)　43-47　1993

DOI： 10.3379/jmsjmag.17.43 　

ISSN： 0285-0192 1880-4004

Show all ︎Show first 5

Books and Other Publications 4

Magnetic Measurement Techniques for Materials Characterization

Satoshi Okamoto (22. Permanent Magnet Materials)

Springer　2021

ISBN: 9783030704421
RF power semiconductor generator application in heating and energy utilization

S. Okamoto

Springer Nature Singapore Pte Ltd　2020
省/脱Dyネオジム磁石と新規永久磁石の開発

岡本聡

(株)シーエムシー出版　2015/06

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薄膜の評価技術ハンドブック

岡本聡

2013/01

Presentations 161

直流バイアス磁場下における各種軟磁性コアの鉄損挙動の特徴解析

大沼智幸, 小野暢久, 岡本聡

日本金属学会2025年春期講演大会　2025/03/10
多結晶軟磁性材料における磁歪効果の結晶粒径依存性

塚原宙, Haodong Huang, 鈴木清策, 小野寛太, 岡本聡

日本金属学会2025年春期講演大会　2025/03/10
High-Frequency Core Loss Reduction in Fe-Based Soft Magnetic Ribbons: A Microstructural Approach Invited

R. Gautam, S. Hiramoto, H. Mamiya, T. Ogasawara, S. Okamoto, T. Ohkubo, H. Sepehri-Amin

The 16th Joint Conference on Magnetism and Magnetic Materials and Intermag　2025/01/16
Novel Approaches of Nanocrystalline Alloys with Large Saturation Magnetization for Next-Generation Power-Electronics Applications Invited

S. Okamoto, A. Urata, H. Oikawa, S. Hiramoto, N. Ono, R. Gautam, H. Sepehri-Amin, T. Ohkubo, T. Ogasawara

The 16th Joint Conference on Magnetism and Magnetic Materials and Intermag　2025/01/15
Soft Magnets Invited

Satoshi Okamoto

The 16th Joint Conference on Magnetism and Magnetic Materials and Intermag　2025/01/14
Physical Origin of Excess Loss due to Magnetostriction in Soft Magnetic Materials Invited

Hiroshi Tsukahara, Haodong Huang, Kiyonori Suzuki, Kato Akira, Kanta Ono, Satoshi Okamoto

ENGE 2024　2024/11/25
Approaches of Ultra-low Loss Soft Magnetic Materials for Next-generation Power Electronics Invited

Satoshi Okamoto

ENGE 2024　2024/11/25
軟磁性材料の基礎について Invited

岡本聡

日本ボンド磁性材料協会(JABM)寺子屋BM塾　2024/10/11
磁化過程に基づく鉄損要因解析と統計モデルの比較

小野暢久, 上原裕二, 大沼智幸, 谷口卓也, 岡本聡

日本磁気学会第48回学術講演会　2024/09/27
各種磁性コアの直流バイアス特性とB-Hカーブ形状の相関

大沼智幸, 小野暢久, 岡本聡

日本磁気学会第48回学術講演会　2024/09/27
Sincパルスを用いた広帯域鉄損機構の調査

谷口卓也, 上原裕二, 佐藤佑樹, 塚原宙, 岡本聡

日本磁気学会第48回学術講演会　2024/09/27
軟磁性材料における過剰損失発生機構の解明 Invited

塚原宙, H. Huang, 鈴木清策, 小野寛太, 岡本聡

日本磁気学会第48回学術講演会　2024/09/27
Effect of nanostructure on the core loss of soft magnetic materials Invited

H. Sepehri-Amin, R. Gautam, A. Bolyachkin, N. Kulesh, S. Hiramoto, H. Mamiya, S. Okamoto, T. Miyatake, T. Ohkubo

日本磁気学会第48回学術講演会　2024/09/27
マイクロ波アシスト磁化反転と磁気的相互作用

菊池伸明, 畑山正寿, 島津武仁, 岡本聡

日本磁気学会第48回学術講演会　2024/09/25
透磁率時間変調メタマテリアルによるマイクロ波周波数変換

児玉俊之, 菊池伸明, 岡本聡, 大野誠吾, 冨田知志

日本磁気学会第48回学術講演会　2024/09/25
Nd-Fe-B 熱間加工磁石の3次元磁化反転過程解析に向けた磁区抽出

諏訪智巳, 鈴木基寛, 大久保忠勝, 入山恭彦, 宮脇寛, 谷口卓也, 岡本聡

日本金属学会2024年秋季講演大会　2024/09/19
永久磁石材料のマルチスケール・マルチモーダル磁化過程解析 Invited

岡本聡

電気学会A部門大会　2024/09/03
混合ガウスモデルとDavies Bouldin基準を用いたFORCダイアグラムのクラスタリング

応瑞軒, 谷口卓也, 鍋田滉希, 石上啓介, 菊池伸明, 岡本聡

マグネティクス研究会　2024/08/09
マイクロ波アシスト磁化反転と磁気的相互作用

菊池伸明, 畑山正寿, 島津武仁, 岡本聡

MRIS研究会　2024/06/06
Iron Loss Behaviors of Various Inductors Under DC Bias Fields

Tomoyuki Onuma, Nobuhisa Ono, Satoshi Okamoto

MORIS2024　2024/05/31
Clustering FORC diagram using Gaussian mixture model and Davies-Bouldin Index

R. Ying, T. Taniguchi, K. Nabeta, K. Ishigami, N. Kikuchi, S. Okamoto

MORIS2024　2024/05/30
Observation of the Magnon Hall Effect of Magnetostatic Forward Volume Spin Waves

Takuya Taniguchi, Christian Riedel, Franz Vilsmeier, Satoshi Okamoto, Christian H. Back

MORIS2024　2024/05/30
正弦波/三角波励磁によるトロイダルコアのコア損失測定

上原裕二, 岡本聡, 佐藤佑樹, 谷口卓也

日本磁気学会第48回学術講演会　2024/05/27
Effect of binder content on structure and magnetic properties of Fe-Si powder cores

Mai Phuong Nguyen, Shigeyoshi Yoshida, Satoshi Okamoto, Takamichi Miyazaki, Yasushi Endo

INTERMAG2024　2024/05/05
物理視点でみる次世代パワエレに向けた軟磁性材料および磁性素子研究の現状と課題 Invited

岡本聡

第92回日本磁気学会スピントロニクス専門研究会　2024/04/24
混合ガウスモデルとベイズ情報量規準を用いたFORCダイアグラムのクラスタリング

応瑞軒, 谷口卓也, 鍋田滉希, 石上啓介, 菊池伸明, 岡本聡

日本金属学会2024年春期講演大会　2024/03/15
Fe-B-P-Cu合金のナノ結晶化その場観察

平本尚三, 岡本聡, 小見山渓太, 森吉千佳子, 黒岩芳弘

日本金属学会2024年春期講演大会　2024/03/14
高周波パワエレ回路用低透磁率材料の鉄損測定の精度検証 Invited

佐藤佑樹, 上原裕二, 岡本聡, 吉田栄吉, 遠藤恭

日本金属学会2024年春期講演大会　2024/03/14
磁化過程に基づく鉄損要因解析と統計モデルの比較

小野暢久, 上原裕二, 大沼智幸, 谷口卓也, 菊池伸明, 岡本聡

日本金属学会2024年春期講演大会　2024/03/14
材料ならびに透磁率の異なる各種磁性コアの直流バイアス特性

大沼智幸, 小野暢久, 岡本聡

日本金属学会2024年春期講演大会　2024/03/14
Core loss reduction of Fe-based amorphous alloys by formation of Cu clusters

R. Gautam, H. Sepehri-Amin, S. Hiramoto, H. Mamiya, S. Okamto, T. Miyatake, T. Ohkubo

日本金属学会2024年春期講演大会　2024/03/14
Core loss reduction of soft magnetic materials by nanostructure engineering Invited

H. Sepehri-Amin, R. Gautam, S. Hiramoto, H. Mamiya, S. Okamto, T. Miyatake, T. Ohkubo

日本金属学会2024年春期講演大会　2024/03/14
Recent progress in soft magnetic composite materials Invited

Mai Phuong Nguyen, Shigeyoshi Yoshida, Satoshi Okamoto, Sho Muroga, Takamichi Miyazaki, Yasushi Endo

日本金属学会2024年春期講演大会　2024/03/14
磁歪によるランダム磁気異方性とエネルギー損失機構の解明

塚原宙, Haodong Huang, 鈴木清策, 小野寛太, 岡本聡

日本金属学会2024年春期講演大会　2024/03/14
Microscopy Studies on Magnetic Domains in a Magnetostrictive Fe-Ga Alloy

Yuto Tomita, Takehiro Tamaoka, Mitsunari Auchi, Yasukazu Murakami, Nobuhisa Ono, Masatoshi Hatayama, Satoshi Okamoto, Yu U. Wang, Yongmei M. Ji

日本金属学会2024年春期講演大会　2024/03/13
磁性材料関連の研究会をふりかえって Invited

岡本聡

アモルファス・ナノ材料と応用第147委員会第155回研究会　2024/03/06
永久磁石・軟磁性材料のデータ駆動型研究 Invited

岡本聡

2023年度学術討論会・技術交流フォーラム　2024/02/08
放射光磁気イメージングによる永久磁⽯材料の磁化過程解析 Invited

岡本聡

磁性材料研究会　2024/01/24
Nd-Fe-B磁石のマルチスケール保磁力解析 Invited

岡本聡

電気学会マグネティックス研究会　2023/12/22
3D Visualization of the Magnetic Domain Structure Inside Advanced Permanent Magnets using X-ray Magnetic Tomography International-presentation Invited

Satoshi Okamoto, Tomomi Suwa, Keisuke Ishigami, Takuya Taniguchi, Motohiro Suzuki

MRM2023/IUMRS-ICA2023　2023/12/15
Current-induced Nonlinear Spin Polarization in Ta/FeNi/Pt Spintronic Metamaterial

T. Kodama, N. Kikuchi, T. Chiba, S. Okamoto, S. Ohno, S. Tomita

CRC-GP-MSSP 2023　2023/11/28
Multiscale and Multimodal Analyses on Coercivity Mechanism of Permanent Magnets Invited

Satoshi Okamoto

KMS 2023 Winter Conference　2023/11/24
Magnetic Imaging Using a Synchrotron Radiation Light Invited

Satoshi Okamoto

IEC-TC51 Meeting　2023/11/16
Magnetic properties of Fe-Ni powder core for high frequency devices applications

Mai Phuong Nguyen, Shigeyoshi Yoshida, Satoshi Okamoto, Takamichi Miyazaki, Yasushi Endo

MMM2023　2023/10/31
Evaluation of structure and magnetic properties in amorphous dust cores for high frequency devices applications

Mai Phuong Nguyen, Shigeyoshi Yoshida, Satoshi Okamoto, Takamichi Miyazaki, Yasushi Endo

MMM2023　2023/10/31
軟磁性研究における課題とインフォマティクスへの展開 Invited

岡本聡, 小嗣真人, 大久保忠勝

日本金属学会　2023/09/21
磁化反転過程に基づく各種トロイダル磁心の鉄損解析

小野暢久, 上原裕二, 遠藤恭, 吉田栄吉, 及川英彦, 菊池伸明, 岡本聡

第47回日本磁気学会学術講演会　2023/09
軟磁性薄帯材料の時間分解ベクトル磁区観察

小笠原剛, 田丸慎吾, 岡本聡

第47回日本磁気学会学術講演会　2023/09
マイクロ波アシスト磁化反転時のエネルギー障壁

水谷聡志, 菊池伸明, 畑山正寿, 島津武仁, 岡本聡

第47回日本磁気学会学術講演会　2023/09
温度・ Dy 添加量・配向度を変化させた Nd–Fe–B 焼結磁石の FORC ダイアグラムの特徴抽出

石上啓介, 鍋田滉希, 古澤大介, 槙智仁, 西内武司, 中村哲也, 岡本聡

第47回日本磁気学会学術講演会　2023/09
ランダウ理論から見た磁化状態の熱安定性と反転磁場

三俣千春, 小嗣真人, 岡本聡

第47回日本磁気学会学術講演会　2023/09
時間変調メタマテリアルに向けたスピン注入透磁率制御

児玉俊之, 清水蓮也, 菊池伸明, 岡本聡, 大野誠吾, 冨田知志

第47回日本磁気学会学術講演会　2023/09
Tb拡散Nd-Fe-B焼結磁石の3次元的な微細組織と磁区構造からの特徴抽出

諏訪智巳, 石上啓介, 鈴木基寛, 岡本聡

第47回日本磁気学会学術講演会　2023/09
圧粉コアの直流バイアス特性と B-H カーブ特徴解析の相関

大沼智幸, 小野暢久, 岡本聡

第47回日本磁気学会学術講演会　2023/09
配向度、Dy組成の異なるNd-Fe-B焼結磁石の FORCダイアグラム測定

鍋田滉希, 石上啓介, 古澤大介, 槙智仁, 西内武司, 岡本聡

第47回日本磁気学会学術講演会　2023/09
Feature extraction of 3D real pictures of microstructure and magnetic domain in a Tb diffused Nd-Fe-B sintered magnet

Tomomi Suwa, Keisuke Ishigami, Motohiro Suzuki, Satoshi Okamoto

REPM2023　2023/09
Understanding the Coercivity of Ga-containing Nd–Fe–B Sintered Magnets from Feature Extraction and Selection of X-ray Diffraction Patterns via Dimension Reduction and Sparse Modeling

Keisuke Ishigami, Tomoyuki Onuma, Akira Kato, Masao Yano, Tetsuya Shoji, Tetsuya Nakamura, Satoshi Okamoto

REPM2023　2023/09
Tb拡散Nd-Fe-B焼結磁石の 3次元微細組織と磁区構造からの特徴抽出

諏訪智巳, 石上啓介, 岡本聡, 鈴木基寛

電気学会マグネティックス研究会　2023/08
マイクロ波アシスト磁化反転と熱揺らぎ

菊池伸明, 佐藤勝成, 水谷聡志, 畑山正寿, 島津武仁, 岡本聡

電子情報通信学会研究会　2023/06
Accuracy Investigation of High-Frequency Core Loss Measurement for Low-Permeability Magnetic Materials

Yuki Sato, Yuji Uehara, Satoshi Okamoto, Shigeyoshi Yoshida, Yasushi Endo, Nobuhisa Ono, Nobuto Misono, Hirokazu Matsumoto

INTERMAG2023　2023/05
Analysis on iron loss of Sendust dust cores based on magnetization reversal processes

Nobuhisa Ono, Yuji Uehara, Yasushi Endo, Shigeyoshi Yoshida, Nobuaki Kikuchi, Satoshi Okamoto

INTERMAG2023　2023/05
Permeability Variation of Ferromagnetic wires for Time-varying Spintronic Metamaterials

Toshiyuki Kodama, Nobuaki Kikuchi, Satoshi Okamoto, Seigo Ohno, Satoshi Tomita

INTERMAG2023　2023/05
Challenges to High Magnetic Flux Density and Low Loss Magnetic Materials and Devices for Next-Generation Power Electronics Invited

Satoshi Okamoto, Nobuhisa Ono, Tomoyuki Onuma, Zhenzhuang Li, Yuji Uehara, Anton Bolyachkin, Hossein Sepehri-Amin, Tadakatsu Ohkubo

INTERMAG2023　2023/05
Evaluation of microstructure and magnetic performance of Fe- 6.5 wt% Si soft magnetic powder core

Mai Phuong Nguyen, Shigeyoshi Yoshida, Satoshi Okamoto, Takamichi Miyazaki, Yasushi Endo

INTERMAG2023　2023/05
Feature Extraction and Selection of X-ray Diffraction Pattern Explaining Coercivity of Ga-containing Nd-Fe-B Sintered Magnets by Sparse Modeling Invited

Keisuke Ishigami, Tomoyuki Onuma, Akira Kato, Masao Yano, Tetsuya Shoji, Tetsuya Nakamura, Satoshi Okamoto

INTERMAG2023　2023/05
Feature analysis on B-H B-H curves of dust cores under the application of DC bias field

Tomoyuki Onuma, Zhenzhuang Li, Satoshi Okamoto

INTERMAG2023　2023/05
Effect of film thickness on microwave assisted switching behavior

Nobuaki Kikuchi, Katsunari Sato, Masatoshi Hatayama, Takehito Shimatsu, Satoshi Okamoto

INTERMAG2023　2023/05
硬X線磁気トモグラフィーによる先端永久磁石の磁気ヒステリシス解析 Invited

岡本聡

2022年度ナノスピントロニクス研究会・機能磁性材料分光研究会合同研究会　2023/03/28
時間変調メタマテリアルに向けたスピン流注入によるCo細線の透磁率制御

清水蓮也, 児玉俊之, 大野誠吾, 菊池伸明, 岡本聡, 冨田知志

応用物理学会春季学術講演会　2023/03/15
時間変調メタマテリアルに向けた NiFe 細線のスピン流誘起透磁率制御

児玉俊之, 大野誠吾, 菊池伸明, 岡本聡, 冨田知志

応用物理学会春季学術講演会　2023/03/15
マイクロ波アシスト磁化反転における熱活性の影響

水谷聡志, 岡本聡

２０２２年度物質・デバイス領域共同研究拠点展開共同研究研究会　2023/03/14
磁化過程分離モデルを用いたセンダスト圧粉磁性コアの鉄損要因解析

小野暢久, 岡本聡

２０２２年度物質・デバイス領域共同研究拠点展開共同研究研究会　2023/03/14
Nd-Fe-B熱間加工磁石の磁区構造ネットワークの解析

諏訪智巳, 岡本聡

２０２２年度物質・デバイス領域共同研究拠点展開共同研究研究会　2023/03/14
圧粉コアの直流バイアス特性における B-H カーブ形状の特徴解析

大沼智幸, 李振庄, 岡本聡

日本金属学会2023年春期(第172回)講演大会　2023/03/09
磁化過程分離モデルを用いたセンダスト圧粉磁性コアの鉄損要因解析

小野暢久, 上原裕二, 遠藤恭, 吉田栄吉, 菊池伸明, 岡本聡

日本金属学会2023年春期(第172回)講演大会　2023/03/09
磁化測定から見えてくる永久磁石の微視的保磁力機構 Invited

岡本聡

NIMS磁石パートナーシップ第9回研究会　2023/02/16
永久磁⽯の磁化過程解析の現在地と今後 Invited

岡本聡

電気学会マグネティックス研究会　2022/12/21
次世代パワエレに向けた高磁束密度・低損失磁性材料およびデバイス創成への挑戦 Invited

岡本聡

INNOPELシンポジウム2022　2022/12/14
革新的パワーエレクトロニクスに向けたバルク軟磁性材料研究 Invited

岡本聡

第12回MaSC 技術交流会 Real Exchange　2022/12/13
革新的パワーエレクトロニクスに向けた磁性材料および磁性デバイス開発 Invited

岡本聡

JABM 日本ボンド磁性材料協会 2022BMシンポジウム　2022/12/02
Permeability Control using Spin-Hall Effects for Time-varying Metamaterials

Toshiyuki Kodama, Hiroyuki Kurosawa, Seigo Ohno, Nobuaki Kikuchi, Masatoshi Hatayama, Satoshi Okamoto, Satoshi Tomita

CRCs6-GPMS5　2022/10/24
Approaches of Ultra-Low Iron Loss in Magnetic Materials and Devices for Power Electronics Invited

Satoshi Okamoto

ICFPM2022　2022/10/20
次世代パワーエレクトロニクスに向けた軟磁性材料および磁気デバイス開発 Invited

岡本聡

日本金属学会2022 年秋期講演　2022/09/21
革新的パワーエレクトロニクスに向けた軟磁性材料およびデバイス開発 Invited

岡本聡

令和4年電気学会基礎・材料・共通部門大会　2022/09/13
ナノスケールハード磁性体の非線形磁化ダイナミクスを利用した次世代磁気記録技術 Invited

岡本聡

令和4年電気学会基礎・材料・共通部門大会　2022/09/13
Sm(Fe80Co20)12エピタキシャル微粒子薄膜の作製

鍋田滉希, 芳賀僚太, 菊池伸明, 高橋有紀子, 岡本聡

第46回日本磁気学会学術講演会　2022/09/08
磁性膜厚のマイクロ波アシスト磁化反転挙動への影響

菊池伸明, 佐藤勝成, 畑山正寿, 島津武仁, 岡本聡

第46回日本磁気学会学術講演会　2022/09/08
マイクロ波アシスト磁化反転における熱活性の影響

水谷聡志, 菊池伸明, 畑山正寿, 島津武仁, 岡本聡

第46回日本磁気学会学術講演会　2022/09/08
2 コイル法と共振法の併用によるセンダスト圧粉コアのブロードバンド鉄損測定

小野暢久, 上原裕二, 遠藤恭, 吉田栄吉, 及川英彦, 菊池伸明, 岡本聡

第46回日本磁気学会学術講演会　2022/09/08
ディスク状微細加工磁性ドットアレイによる高周波電磁波吸収材特性

彭牧天, 大沼智幸, 畑山正寿, 菊池伸明, 田丸慎吾, 岡本聡

2022/09/06
透磁率時間変調メタマテリアルを用いたマイクロ波の周波数変換

児玉俊之, 黒澤裕之, 大野誠吾, 菊池伸明, 畑山正寿, 岡本聡, 冨田知志

第46回日本磁気学会学術講演会　2022/09/06
COBALT/PLATINUM SUPERLATTICE FOR TIME-VARYING METAMATERIALS

Satoshi Tomita, Nobuaki Kikuchi, Satoshi Okamoto

MORIS2022　2022/05/17
THERMAL ACTIVATION ON MICROWAVE ASSISTED MAGNETIZATION SWITCHING IN Co/Pt NANODOT ARRAYS

S. Mizutani, N. Kikuchi, M. Hatayama, T. Shimatsu, S. Okamoto

2022/05/17
Microwave assisted switching in granular media with continuous cap layers for interaction control

N. Kikuchi, K. Sato, T. Shimatsu, O. Kitakami, S. Okamoto

2022/05/17
Ultra-low loss magnetic materials for innovative power electronics Invited

Satoshi Okamoto

International Power Electronics Conference, IPEC-Himeji 2022　2022/05/16
永久磁石材料におけるマルチスケール磁化過程解析 Invited

岡本聡

電気学会全国大会　2022/03/23
極微細粒Nd-Fe-B焼結磁石を用いたヒステリシス3次元磁区観察

岡本聡, 竹内誠, 小林慎太郎, 小谷佳範, 中村哲也, 菊池伸明, A. Bolyachkin, H. Sepehri-Amin, 大久保忠勝, 宝野和博, 宇根康裕, 鈴木基寛

日本金属学会2022年春期講演大会　2022/03/15
Physical origin of bimodal complex permeability spectrum of a noise-suppression sheet

T. Igarashi, S. Tamaru, N. Kikuchi, S. Yoshida, S. Okamoto

2022 Joint MMM-INTERMAG　2022/01/12
Co/Pt ナノドットを用いたマイクロ波アシスト磁化反転における熱活性の影響

水谷聡志, 菊池伸明, 畑山正寿, 島津武仁, 岡本聡

２０２１年度物質・デバイス領域共同研究拠点展開共同研究Ｂ　2021/12/28
Sm(FeCo)12 微粒子薄膜の作製と高保磁力発現の検討

芳賀僚太, 高橋有紀子, 菊池伸明, 岡本聡

２０２１年度物質・デバイス領域共同研究拠点展開共同研究Ｂ　2021/12/28
先端永久磁石材料のヒステリシス 3 次元磁区計測

岡本聡

２０２１年度物質・デバイス領域共同研究拠点展開共同研究Ｂ　2021/12/28
3D magnetic domain imaging along magnetic hysteresis using a Tb-Cu diffused Nd-Fe-B PLP magnet Invited

Satoshi Okamoto

CMSM-ESICMM Permanent Magnet Seminar　2021/12/17
永久磁石における微視的保磁力解析

岡本聡

電気学会マグネティックス研究会　2021/12/16
Fe単一扁平粒子の透磁率スペクトルの粒径依存性

大沼智幸, 五十嵐利行, 田丸慎吾, 菊池伸明, 吉田栄吉, 岡本聡

第21回多元物質科学研究所研究発表会　2021/12/09
Magnetic-tomography measurement on a Nd-Fe-B magnet Invited

Satoshi Okamoto

The 3rd International Joint Symposium of 5-star Alliance (Japan), CEFMSNCTU, RCAS-AS (Taiwan)　2021/11/17
Thermal activation on microwave assisted magnetization switching in Co/Pt nanodot arrays

S. Mizutani, N. Kikuchi, M. Hatayama, T. Shimatsu, S. Okamoto

The 5th Symposium for The Core Research Clusters for Materials Science and Spintronics, and the 4th Symposium on International Joint Graduate Program in Materials Science　2021/10/25
Fe単一扁平粒子の透磁率スペクトルの粒径依存性

大沼智幸, 五十嵐利行, 田丸慎吾, 菊池伸明, 吉田栄吉, 岡本聡

第45回日本磁気学会学術講演会　2021/09/01
ノイズ抑制シートにおける bimodal型複素透磁率スペクトルメカニズム

五十嵐利行, 田丸慎吾, 菊池伸明, 吉田栄吉, 岡本聡

第45回日本磁気学会学術講演会　2021/09/01
Co/Pt多層膜ナノドットのマイクロ波アシスト磁化反転における熱活性

水谷聡志, 菊池伸明, 畑山正寿, 島津武仁, 岡本聡

第45回日本磁気学会学術講演会　2021/08/31
極薄化によるSm(Fe80Co20)12微粒子薄膜の作製と保磁力発現可能性の検討

芳賀僚太, 菊池伸明, 岡本聡, 高橋有紀子

電気学会マグネティックス研究会　2021/08/06
Co/Pt多層膜ナノドットのマイクロ波アシスト磁化反転における熱活性の影響

水谷聡志, 菊池伸明, 畑山正寿, 岡本聡, 島津武仁

磁気記録・情報ストレージ研究会　2021/06/10
Spin dynamics of magnetic devices Invited

Satoshi Okamoto

EPSRC International Network for Spintronics Research Symposium　2021/06/09
Sm(Fe80Co20)12の孤立微粒子薄膜の作製と保磁力発現の検討

芳賀僚太, 竹内誠, 菊池伸明, 高橋有紀子, 岡本聡

日本金属学会2021年春期講演大会　2021/03/19
マイクロ波アシスト磁化反転における熱揺らぎの影響 Invited

岡本聡, 菊池伸明, 島津武仁

スピントロニクス学術研究基盤と連携ネットワーク拠点年次報告会　2021/03/09
Field Angle Effect on Microwave Assisted Magnetization Switching

Nobuaki KIKUCHI, Satoshi OKAMOTO, Takehito SHIMATSU

The 4th International Symposium for The Core Research Cluster for Spintronics　2021/02/24
Frequency-domain microwave spectroscopy of Co/Pt superlattice metamaterials

Satoshi Tomita, Nobuaki Kikuchi, Masatoshi Hatayama, Satoshi Okamoto

The 4th International Symposium for The Core Research Cluster for Spintronics　2021/02/24
ナノビーム XMCDを用いた HDD書き込みヘッドの磁化ダイナミクス観察

首藤浩文, 喜々津哲, 小谷佳範, 前田知幸, 豊木研太郎, 大沢仁志, 菊池伸明, 岡本聡

第44回日本磁気学会学術講演会　2020/12/17
磁場印加角度のマイクロ波アシスト磁化反転への影響

菊池伸明, 岡本聡

第44回日本磁気学会学術講演会　2020/12/17
Co/Pt多層膜のコプラナー導波路強磁性共鳴

冨田知志, 菊池伸明, 畑山正寿, 岡本聡

第44回日本磁気学会学術講演会　2020/12/16
Visualization of the magnetization reversal processes in He jet-milled Nd-Fe-B sintered magnet by X-ray magnetic tomography Invited

M. Suzuki, M. Takeuchi, S. Kobayashi, R. Haga, Y. Kotani, T. Nakamura, N. Kikuchi, T. Sasaki, T. Ohkubo, Y. Une, S. Okamoto

2020/12/16
時間・空間的マルチスケール磁気機能解析とデバイス応用 Invited

岡本聡

第20回多元研発表会　2020/12/08
硬X線磁気トモグラフィによる極微細粒Nd-Fe-B焼結磁石の三次元磁区観察

竹内誠, 芳賀僚太, 菊池伸明, 岡本聡, 鈴木基寛, 小林慎太郎, 中村哲也, 大久保忠勝, 埋橋淳, 宇根康裕

マグネティックス研究会　2020/12/08
時間・空間的マルチスケール磁気機能解析とデバイス応用

岡本聡

展開共同研究Ａ研究会　2020/12/02
SmFe12およびSm(Fe-X)12 (X = Ti, Co)エピタキシャル微粒子薄膜の作製と保磁力発現の検討

芳賀僚太, 近藤司, 竹内誠, 菊池伸明, 岡本聡

日本金属学会2020年秋期講演大会　2020/09/18
Tb 添加 He ジェットミル Nd-Fe-B 焼結磁石の FORC 解析

竹内誠, 芳賀僚太, 菊池伸明, 岡本聡, 鈴木基寛, 小林慎太郎, 中村哲也, 宇根康裕

日本金属学会2020年秋期講演大会　2020/09/18
Microwave-Assisted Magnetization Switching Behaviors in Granular Media Invited

S. Okamoto, N. Kikuchi, T. Shimatsu

The Magnetic Recording Conference (TMRC)　2020/08/19
NdFeB熱間加工磁石の単一粒子磁化反転計測と熱揺らぎ解析

蓬田貴裕, 岡本聡, 菊池伸明, 北上修, H. Sepehri-Amin, 大久保忠勝, 宝野和博, 日置敬子, 服部篤

日本金属学会2020年春期講演大会　2020/03/17
X線磁気トモグラフィー測定に向けたHeジェットミルNd-Fe-B焼結磁石の微細加工ならびに磁気特性評価

竹内誠, 蓬田貴裕, 菊池伸明, 岡本聡, 北上修, 鈴木基寛, 小林慎太郎, 中村哲也, 宇根康裕

日本金属学会2020年春期講演大会　2020/03/17
X線磁気トモグラフィーによる微細粒Nd-Fe-B焼結磁石の磁化反転過程の観察

鈴木基寛, 小林慎太郎, 中村哲也, 竹内誠, 蓬田貴裕, 菊池伸明, 岡本聡, 北上修, 宇根康裕

日本金属学会2020年春期講演大会　2020/03/17
永久磁石材料の磁化反転解析 Invited

岡本聡

磁性材料の最新評価・技術セミナ　2020/02/14
永久磁石材料における磁化反転素過程の検出と磁化反転機構解析

岡本聡

元素戦略シンポジウム　2020/02/03
永久磁石材料の磁化反転素過程に関する高感度計測と機構解析

岡本聡

展開共同研究B研究会　2019/12/23
W下地を⽤いたSm(Fe,Ti)12エピタキシャル微粒⼦薄膜の作製

近藤司, 岡本聡, 菊池伸明, 芳賀僚太, 北上修

電気学会マグネティクス研究会　2019/12/19
CoCrPtグラニュラー薄膜における磁性粒⼦間交換結合のマイクロ波アシスト磁化反転への影響

佐藤勝成, 菊池伸明, 岡本聡, 北上修, 島津武仁

電気学会マグネティクス研究会　2019/12/19
Temperature dependent magnetization reversal process of a Ga-doped Nd-Fe-B sintered magnet based on first-order reversal curve analysis

S. Okamoto, K. Miyazawa, T. Yomogita, N. Kikuchi, O. Kitakami, K. Toyoki, D. Billington, Y. Kotani, T. Nakamura, T. Sasaki, T. Ohkubo, K. Hono, Y. Takada, T. Sato, Y. Kaneko, A. Kato

2019/12/12
磁石材料における保磁力機構と磁化反転解析 Invited

岡本聡

東北大学-DOWA技術者交流会　2019/11/18
Detection of elemental magnetization reversal events in a micropatterned hot-deformed Nd-Fe-B magnet

T. Yomogita, N. Kikuchi, S. Okamoto, O. Kitakami, H. Sepheri-Amin, T. Ohkubo, K. Hono, K. Hioki, A. Hattori

64th Annual Conference on Magnetism and Magnetic Materials　2019/11/04
Ultra-broadband and ultra-high sensitivity permeability measurements by transformer coupled permeameter International-presentation

S. Tamaru, H. Kubota, N. Kikuchi, S. Okamoto

64th Annual Conference on Magnetism and Magnetic Materials　2019/11/04
Temperature dependent magnetization reversal process of a Ga-doped Nd-Fe-B sintered magnet based on first-order reversal curve analysis International-presentation

S. Okamoto, K. Miyazawa, T. Yomogita, N. Kikuchi, O. Kitakami, K. Toyoki, D. Billington, Y. Kotani, T. Nakamura, T. Sasaki, T. Ohkubo, K. Hono, Y. Takada, T. Sato, Y. Kaneko, A. Kato

64th Annual Conference on Magnetism and Magnetic Materials　2019/11/04
保磁力機構解析の新手法と材料開発への適用 Invited

岡本聡

NIMS磁石パートナーシップ第３回研究会　2019/11/01
永久磁石材料における保磁力解析と磁化反転機構 Invited

岡本聡

粉体粉末冶金協会2019年度秋季大会　2019/10/22
Transient magnetization dynamics of a Co/Pt multilayer dot probed by XMCD International-presentation Invited

N. Kikuchi, S. Okamoto, O. Kitakami, H. Osawa, M. Suzuki

The 19th International Conference on Solid Films and Surfaces　2019/10/06
軟X線MCD/走査プローブ顕微鏡を用いたスキルミオン観察 Invited

岡本聡

第 9 回実用スピントロニクス新分野創成研究会　2019/10/02
CoCrPtグラニュラ薄膜における粒子間交換結合のマイクロ波アシスト磁化反転への影響

佐藤勝成, 菊池伸明, 岡本聡, 北上修, 島津武仁

第43回⽇本磁気学会学術講演会　2019/09/25
Sm(Fe,Ti)12エピタキシャル微粒子薄膜の作製

近藤司, 岡本聡, 菊池伸明, 北上修

第43回⽇本磁気学会学術講演会　2019/09/25
軟 X 線 MCD 顕微分光による熱間加工磁石の磁化過程評価

竹内誠, 蓬田貴裕, 菊池伸明, 岡本聡, 北上修, 豊木研太郎, 小林慎太郎, 小谷佳範, 中村哲也, 服部篤, 日置敬子

第43回⽇本磁気学会学術講演会　2019/09/25
微細加工した熱間加工Nd-Fe-B磁石の磁化反転素過程計測

蓬田貴裕, 菊池伸明, 岡本聡, 北上修, H. Sepehri-Amin, 大久保忠勝, 宝野和博, 日置敬子, 服部篤

第43回⽇本磁気学会学術講演会　2019/09/25
Development of synchrotron X-ray nano-beam dynamic force microscope Invited

H. Nomura, R. Wakasa, N. Samura, Y. Jibiki, K. Takahashi, S. Miki, J. Yamaguchi, R. Nakatani, M. Goto, Y. Suzuki, K. Toyoki, N. Kikuchi, S. Okamoto, Y. Kotani, T. Nakamura

2019/09/25
Nd-Fe-B 焼結磁石の FORC 解析

宮澤和則, 岡本聡, 蓬田貴裕, 菊池伸明, 北上修

電気学会A部門大会　2019/09/04
マイクロ波アシスト磁化反転と磁気記録への応用 Invited

岡本聡, 菊池伸明, 北上修, 島津武仁

第12回光・熱・磁気の相互作用を利用した新規スピンデバイス・ストレージ技術調査専門委員会　2019/08/30
軟X線MCD顕微分光による熱間加工磁石の磁化過程観察

竹内誠, 蓬田貴裕, 菊池伸明, 岡本聡, 北上修, 豊木研太郎, 小林慎太郎, 小谷佳範, 中村哲也, 服部篤, 日置敬子

電気学会マグネティクス研究会　2019/08/08
次世代スピントロニクスに向けた磁性体薄膜の材料設計

中村浩次, A.-M. Pradipto, 菊池伸明, 岡本聡, 北上修, 籾田浩義, 山内邦彦, 小口多美夫, 藤枝俊

展開B研究会　2019/07/01
SPATIALLY-, TEMPORALLY-, AND ELEMENTALLY-RESOLVED IMAGING OF MAGNETIZATION DYNAMICS WITH X-RAY MAGNETIC CIRCULAR DICHROISM International-presentation

N. Kikuchi, T. Yomogita, K. Sato, S. Okamoto, O. Kitakami, H. Osawa, M. Suzuki, Y. Kotani, K. Toyoki, T. Nakamura

Magnetics and Optics Research International Symposium　2019/06/23
Microwave assisted switching on CoPtCr-based granular media International-presentation Invited

N. Kikuchi, K. Sato, S. Okamoto, O. Kitakami, T. Shimatsu

Magnetics and Optics Research International Symposium　2019/06/23
CoCrPtグラニュラ記録媒体のマイクロ波アシスト磁化反転実験

佐藤勝成, 菊池伸明, 岡本聡, 北上修, 島津武仁

磁気記録・情報ストレージ研究会　2019/06/13
熱間加工Nd-Fe-B磁石の微細加工による単一磁化反転計測

蓬田貴裕, 岡本聡, 菊池伸明, 北上修, H. Sepehri-Amin, 大久保忠勝, 宝野和,博, 服部篤, 日置敬子

日本金属学会 2019年春期大会　2019/03/22
Nd-Fe-B焼結磁石のFORC diagramにおける定量解析

宮澤和則, 岡本聡, 菊池伸明, 北上修, 佐々木泰祐, 大久保忠勝, 宝野和博, 高田幸生, 佐藤岳, 金子裕治, 加藤晃

日本金属学会 2019年春期大会　2019/03/22
マイクロ波アシスト磁気記録における磁化反転挙動 Invited

岡本聡, 菊池伸明, 北上修, 島津武仁

電気学会全国大会　2019/03/12
コプレーナ線路を用いたPy/Ag/Bi三層膜の強磁性共鳴

川崎連, 妹尾駿一, 岡本聡, 菊池伸明, 北上修, 冨田知志, 細糸信好, 柳久雄

第66回応用物理学会春季学術講演会　2019/03/09
マイクロ波アシスト磁気記録における磁化反転機構

岡本聡, 菊池伸明, 北上修, 島津武仁

電子情報通信学会研究会　2019/03/08
Thermal activation effect in microwave assisted switching of CoCrPt granular media International-presentation

N. Kikuchi, S. Kikuchi, K. Shimada, K. Sato, S. Okamoto, O. Kitakami, T. Shimatsu

The 14th Joint MMM-Intermag Conference　2019/01/14

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Research Projects 18

保磁力理論研究の新展開：原子スケールの揺らぎを保持したマルチスケール解析法の開発

西野正理, 宮下精二, 岡本聡

Offer Organization: 日本学術振興会

System: 科学研究費助成事業

Category: 基盤研究(B)

Institution: 国立研究開発法人物質・材料研究機構

2024/04/01 - 2027/03/31
Research of synthetic antiferromagnet for THz devices with Brillouin light scattering

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (B)

Institution: Tohoku University

2021/04/01 - 2024/03/31
軟磁性微粒子の高周波帯域における磁気損失の起源解明とその設計手法の開発

岡本聡, 島津武仁, 吉田栄吉, 田丸慎吾, 菊池伸明

Offer Organization: 日本学術振興会

System: 科学研究費助成事業

Category: 基盤研究(B)

Institution: 東北大学

2020/04/01 - 2023/03/31

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5G通信における信号品質の確保やパワーデバイスのスイッチング周波数の高周波化に伴い、MHzからGHz帯域での軟磁性微粒子の磁気損失制御が重要な課題となっている。現状ではデバイス実装が先行しており、この周波数帯域における磁気損失に関する学術的理解はほとんど進んでいない。これまでは軟磁性微粒子の集合組織での特性が評価されてきたのみであるが、本研究においては、その構成要素である単一軟磁性微粒子の高周波特性を詳細に調べ、その磁気損失の起源解明を第一の目的としている。次に、この単一軟磁性微粒子の結果を集合組織に反映させる理論モデルを構築し、集合組織として所望の磁気損失特性を実現する設計手法の確立を第二の目的としている。本研究の成果は、今後の高速通信やパワーデバイスに大きく貢献するものである。本年度はSPring-8のXMCD顕微計測を用いて単一扁平磁性粒子の磁化状態観察を行った。その結果、理想的な磁気Vortex構造ではないものの、flux closure状態が複数形成されており、前年度までの低周波領域と高周波領域の吸収ピークに対応する磁化状態であることを確認した。次にトランス結合型透磁率計を用いて、扁平磁性粒子の透磁率スペクトルの粒子サイズ依存性を詳細に計測した。その結果、これまでの低周波領域と高周波領域の吸収ピークだけでなく、中間周波数領域にも吸収ピークが存在していることが分かった。低周波領域の吸収ピークはVortexコアの周回運動で、高周波領域の吸収ピークは磁気Vortex周辺部の一斉励起であるflux closureモードで説明できるが、それに加えて各flux closure状態における一斉励起モードで中間周波数領域の吸収ピークが説明できることが分かった。
Engineering technology for high frequency spin dynamics

Okamoto Satoshi

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (B)

Institution: Tohoku University

2017/04/01 - 2020/03/31

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High frequency spin dynamics has been intensely studied in many fields such as spintronics and magnetic recording. The main purpose of this study has been to develop engineering technology of high frequency spin dynamics. As an example of this issue, we have investigated the next-generation magnetic recording technology based on high frequency spin dynamics using samples with various inter-layer and inter-granular exchange coupling. Consequently, we have successfully found that the magnetization reversal behavior under the application of microwave fields can be well controlled by varying the magnetic coupled mode of the sample.
Magnetization reversal analysis of permanent magnet considering local demagnetizing field

Kitakami Osamu

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (B)

Institution: Tohoku University

2017/04/01 - 2020/03/31

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NdFeB magnets play crucial roles in modern technologies, such as electric vehicles and power generators. At high operation temperatures, however, the performance severely deteriorates due to the coercivity decay. The aim of the present study is to clarify how one can enhance the coercivity by revealing the magnetization process. We have carefully traced elementary magnetization processes occurring in single nanostructured NdFeB magnets consisting of a few magnetic domains by means of the highly sensitive magnetization detection technique and the x-ray circular dichroism. It has been found that the magnetization proceeds by domain wall displacement and the coercivity is dominated by the pinning of the domain walls at crystal grain boundaries. According to the micromagnetics simulation as well as the experiment mentioned above, the coercivity is found to be effectively enhanced by weakening the exchange stiffness of the boundary phase.
Feasibility study on multilevel memory based on skyrmion dynamics

Okamoto Satoshi, Sato Rie

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Challenging Research (Exploratory)

Institution: Tohoku University

2017/06/30 - 2019/03/31

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We studied the feasibility of a novel multilevel memory device based on skyrmion which has recently attracted much attention as one of the topological spin structures. We firstly studied the condition for the stable existence of skyrmion on a magnetic thin film through the micromagnetic calculations. Next, under thus determined stable condition of skyrmion, we explored the microwave response of the skyrmions. Consequently, we successfully demonstrated that generation and erasing of skyrmions inside the magnetic disk was possible by applying a microwave pulse. We had tried to study the microwave response of skyrmions experimentally. For this purpose, we fabricated a device using a GdFeCo amorphous alloy thin film. Unfortunately, it was difficult to observe the skyrmions on the GaFeCo amorphous disk. However, the control of magnetization direction by applying the microwave was clearly confirmed as a fundamental operation of skyrmion memory.
Study of visualization of nano-magnetic dynamics and the development of the experimental techniques using synchrotron radiation

Nakamura Tetsuya

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (A)

Institution: Japan Synchrotron Radiation Research Institute

2015/04/01 - 2018/03/31

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We have studied the synchrotron X-ray magnetic circular dichroism (XMCD) measurement techniques using the nano-focused X-ray beam and the application to magnetic thins films. The time resolved XMCD signals have been successfully observed for the local area of about 100 nm in a Co/Pt multilayered film, where the applied magnetic fields were generated and synchronized with the pulsed X-rays. As a further advanced technical challenge, we have developed a scanning probe microscope (SPM) measurement technique combined with the synchrotron soft X-rays, which is so called SR-SPM. In the SR-SPM apparatus equipped with an X-ray focusing unit using a Fresnel zone plate, the higher density soft X-ray beam of about 1000 times compared to the previous studies irradiates the sample surface just below the SPM needle. XMCD signals from permalloy dots of the magnetite has been successfully recorded using the SR-SPM system with the special resolution of about 70 nm.
Development of high-efficiency techniques of microwave-assisted magnetization switching

Okamoto Satoshi, SATO KIMINORI

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (B)

Institution: Tohoku University

2014/04/01 - 2017/03/31

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In this study, we have investigated various approaches to improve the efficiency of microwave-assisted magnetization switching effect. First, we successfully developed novel quantitative evaluation methods for large cone angle magnetization precession in a nano-scale magnetic dot based on anomalous Hall effect (AHE) and x-ray magnetic circular dichroism (XMCD) detection techniques. Then, we studied the microwave-assisted magnetization switching against various factors, such as the interlayer coupling in a dot composed of two magnetic layers, the effective gyromagnetic ratio in ferromagnetic materials, and inter-grain magnetic interaction in granular magnetic films. It is well verified that these factors can be significantly modify the microwave-assisted switching behavior. These findings are beneficial for practical application of the microwave-assisted magnetization switching.
Magnetization dynamics in microstructed NdFeB single dot

KITAKAMI Osamu, OKAMOTO Satoshi, KIKUCHI Nobuaki, SHIMATSU Takehito, YANAGIHARA Mihiro

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (B)

Institution: Tohoku University

2012/04/01 - 2015/03/31

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The aim of this study is to elucidate the magnetization dynamics of single NdFeB dot. By combining our highly sensitive Hall effect magnetometry with the newly developed large amplitude ns pulse field generator, we have traced magnetization reversal process in single dot after application of slowly varying dc fields and ns pulse fields. Nucleation of reversed domains of about 100 nm in diameter takes place at same points for both cases, but the significant difference is observed in their following expansion. In the dc field case, neighboring nucleated domains are linked to each other, resulting in a maze-like domain structure, while nucleated domains tend to expand isotropically in the pulse field case. Such difference depending on application fields can be explained by assuming multiple energy barriers for magnetization reversal. This result leads us to believe that elimination of defects or something which lower the energy barrier contributes to the enhancement of coercivity.
Precessional switching on perpendicularly magnetized nanodots by picosecond pulse fields

KIKUCHI Nobuaki, KITAKAMI Osamu, OKAMOTO Satoshi

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Young Scientists (A)

Institution: Tohoku University

2012/04/01 - 2015/03/31

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New magnetization reversal methods can be realized by using the effect of magnetization dynamics, in which both magnetization and magnetic field are treated as time dependent terms. In this study, magnetization reversal experiments was carried out based on large angle precessional motion of magnetization produced by applying pulse field normal to the magnetization. Both experiments and calculation results showed that magnetization reversal field can be reduced down to 70 % of that in a static field by using pulse fields with rise time shorter than the relaxation time of magnetization.
Magnetization switching under the assistance of rf field and its feasiility for high density recording

OKAMOTO Satoshi, KIKUCHI Nobuaki, SHIMATSU Takehito, KATO Takeshi

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (B)

Institution: Tohoku University

2011/04/01 - 2014/03/31

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In this study, magnetization switching behaviors of perpendicular magnetic nanodots under the rf field have been investigated and discussed the technological feasibility for the future ultra-high density magnetic recording. Even for the dot 10 times larger than the exchange length, it is reveled that the magnetization switching caused by the precessional motion of whole spins inside the dot is realized. The switching field which is the dc field required for the magnetization switching proportionally decreases with increasing the frequency of the rf field. This switching behavior is well understood by the frequency dispersion of the eignemode of precessional motion which strongly depends on the dot size. These results will provide the novel recording technology which possesses very good controllability.
超高密度磁気記録を可能とする多値記録方式の原理に関する研究

岡本聡, 北上修, 菊池伸明

Offer Organization: 日本学術振興会

System: 科学研究費助成事業

Category: 挑戦的萌芽研究

Institution: 東北大学

2008 - 2009

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磁気記録は原理的な記録密度の限界を迎えつつあり,新規方式の開発が急務となっている.多値記録方式はビット占有面積を小さくすることなく記録密度を増大させることが可能であり,原理的に超高密度化に適しているが,その実現のためには記録の安定性に加えて,現行もしくは将来技術に対する整合性が不可欠である.本研究では,新原理に基づいた安定な多値記録方式の原理実証を目指す.当初の予定では,反強磁性体と強磁性体の界面に生ずる交換結合を利用した反強磁性体/強磁性体の積層構造型の媒体のみを対象としていたが,それに加えて,マイクロ波アシスト方式による多値記録の可能性についても併せて検討を行った. まず良質な反強磁性エピタキシャル薄膜の形成条件の検討を行い,酸化物系として代表的なNiO,CoO,PtMnをMgO(100)基板上に単相成長させることに成功した.それらのエピタキシャル反強磁性薄膜と強磁性Coとの積層構造膜を作製し,その磁気特性ならびに交換結合の評価を行った.さらに微細加工技術によりナノスケールの加工を施すことにより,特性長と交換結合の相関についても検討を行った.次に,新規記録方式として注目されるマイクロ波アシスト方式の原理的な計算を行い,そのスイッチング機構について考察した.検討の結果,本手法ではマイクロ波周波数と外部磁場をパラメータとすることにより,十分に安定な多値記録方式として可能性があることが分かった.今後,マイクロ波アシストを用いた多値記録に適した媒体材料,構造などについて検討を進める予定である.
Study on giant magnetic anisotropy of thin films for magnetic recording

KITAKAMI Osamu, OKAMOTO Satoshi, KIKUCHI Nobuaki, SHIMATSU Takehito, YANAGIHARA Mihiro

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (B)

Institution: Tohoku University

2007 - 2008
Direct observation of ultra-fast switching behavior of a single nanomagnet and development of a new switching technology.

OKAMOTO Satoshi, KITAKAMI Osamu, KIKUCHI Nobuaki

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Young Scientists (A)

Institution: Tohoku University

2006 - 2008
ELECTROMAGNETIC PROPERTIES AND APPLICATION TO MICRO-EMC OF THE METAL-OXIDE COMPOSITE FILMS WITH A FIBER LIKE NANO-STRUCTURE

SHIMADA Yutaka, OKAMOTO Satoshi

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (B)

Institution: TOHOKU UNIVERSITY

2003 - 2004

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Studies were made on granular thin films fabricated by co-evaporation instead of sputtering in order to improve industrious applicability and production efficiency. A few advantages of evaporative deposition were clarified and an improved performance at high frequencies was confirmed in this study. The subjects studied are : 1.Fabrication and search of magnetic anisotropy in Ni80Fe20-(CaF2, SrF2, MgF2, B203). 2.Magnetization process of the fiber structure. 3.How to control phase separation and permeability. 4.TMR associated with the fiber structure. 5.Permeability at high frequencies. 6.Evaluation of the films as EMC materials. The results we have attained in the study are : (1)The fiber structure gives rise to either perpendicular anisotropy or inplane anisotropy depending on the degree of phase separation. (2)Poor TMR is observed for all the samples suggesting that the fiber structure is still in an imperfect phase separation state. (3)The films exhibit good frequency profiles of permeability. Some of the samples such as Ni8OFe20-(CaF2, B203) have resistivity higher than that of usual granular films by two orders. (4)Very high deposition rate (3 orders higher than sputtering) with lower substrate temperature is possible by evaporation. (5)The films with thickness of 2 microns exhibit almost the same performance in suppression and absorption of electromagnetic conductive noise and radiation noise in comparison with 100 micron thick conventional noise suppression sheets. In summary the evaporation process is promising in commercial production of granular materials for various kinds of high frequency applications.
MAGNETIC PROPERTIES OF REGULARLY ARRAYED NANODOTS AND THEIR APPLICATION TO ULTRA-HIGH DENSITY

KITAKAMI Osamu, FUKAMICHI Kazuaki, SHIMADA Yutaka, OKAMOTO Satoshi

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (B)

Institution: TOHOKU UNIVERSITY

2001 - 2003

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In a future ultra-high density magnetic memory, the size of each memory bit will be reduced down to 10×10 nm^2, indicating that each bit consists of one nanoparticle. Therefore, the magnetization reversal process and thermal stability of each nanoparticle have to be clarified for development for the future magnetic memory. However, it has been difficult to measure the magnetic properties of such a nanoparticle because of the very poor sensitivity of 10^<-6> emu for conventional magnetometers. To overcome this difficulty, we have developed a very sensitive Hall effect method for a very small nanoparticle. The sensitivity reaches 〜 10^<-14> emu for FePt. By using this technique, we have investigated the magnetic properties and thermal stability of a single crystal L1_0-FePt (001) nanodot by patterning an well characterized epitaxial film. For the particle diameter of D_m < 20 nm, all the magnetic properties, such as the angular dependence of the irreversible switching field H_r, the magnitude of coercivity H_c, and their temperature dependences, are completely explained by the coherent rotation model (Stoner-Wohlfarth model) taking thermal relaxation into account. As the particle size D_m exceeds 20 nm, the magnetic behaviors obviously deviate from the coherent rotation model, indicating that the magnetization reversal mode changes from coherent to incoherent rotation modes. For this incoherent region, the activation energy has been evaluated to be about 10^<-12> erg regardless of the dot size, which is much smaller than the product of the anisotropy energy and dot volume but nearly equal to γδ^2 (γ: domain wall energy density, δ: wall width), suggesting that the magnetization reversal is initiated by nucleation of a reversed embryo with the dimension of the exchange length. The critical diameter D_m 〜 20 nm at which the reversal mode changes almost agrees with the critical diameter predicted by the micromagnetic theory. Based on these results, we have successfully designed the detail specifications for a prospective ultra-high density magnetic memory with the area density of 1 terabits/inch^2.
強磁性金属/(酸化物,窒化物,水素化物)人工格子による巨大表面磁気異方性の探索

岡本聡

Offer Organization: 日本学術振興会

System: 科学研究費助成事業

Category: 若手研究(B)

Institution: 東北大学

2001 - 2002

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本研究は超薄膜領域の磁性金属からなる種々の人工格子膜を作製し,それらの磁気特性の評価から,ナノ領域において磁気エネルギー増大に極めて効果のある高い表面磁気異方性を有する系を見出すことを目的として行った.試料作製には超高真空DC, RF多元スパッタ装置を用いた.まず,次世代の超高密度磁気記録媒体として期待されているCo/Pd人工格子膜での表面磁気異方性のエンハンスメント効果について調べ,Pd層の水素化ならびに希土類元素(Sm)の添加効果について検討を行った.その結果,水素化に関しては2倍以上にも達する表面磁気異方性の増大が確認され,また希土類添加においても40%近い増大が見出された.これらの結果は,Co/Pd人工格子膜の基本的な磁気特性を変化させることなく,表面磁気異方性を高める手段として上記手法が有効であることを示すものである.次に,磁性金属/酸化物系の組み合わせとして,M/0人工格子膜(M=Fe, Co, Ni, O=SiO_2,MgO)を作製し,その構造ならびに磁気特性の評価を行った.O=MgOの場合には,極低温領域(50K以下)において磁化曲線の非対称性が観測され,僅かではあるが界面酸化層の形成が示唆される結果となった.一方,O=SiO_2の場合にはこのような非対称性は見られず,良好な金属/酸化物の界面が形成されていることを確認した.この系においてはM=Feにおいて最大の表面磁気異方性が得られ,その方向は膜面垂直方向であることが分かった.さらにM=Fe, Co, Niの順に表面磁気異方性は減少しており,磁性金属の3d電子数との強い相関が見出された. 以上の成果は,表面磁気異方性の大きさ及び方向を制御する手法を与えるものとして,ナノ領域の磁気特性制御,更には将来の磁気記録媒体における材料設計に新たな指針を提供するものである.
Development of Magnetic Nanopartides with High Surface Anisotropy for High Density Recording

KITAKAMI Osamu, SHIMADA Yutaka, OKAMOTO Satoshi

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (C)

Institution: Tohoku University

2001 - 2002

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We have studied magnetic surface anisotropy (MSA) at 3d transition metals (TM)/Pd, Pt, SiO_2 interfaces, and investigated the surface effect on the effective magnetic anisotropy of nanopartocles. 1. MSA at TM/Pd, Pt, interfaces The MSA strongly depends on the valence electron number of TM and reaches a maximum of 〜0.5 erg/cm^2 for TM = Co, which is consistent with the first principles calculation so far reportd. R is also found that addition of very small amount of rare earth elements (RE) into TM omsiderahly enhanoes the MSA due to the enhancement of orbital moment of Co. 2. MSA at TM/nonmagnetic oxide (SiO_2) The MSA at TM/SiO_2 strongly depends on the valence electron number of TM. With increasing the valence electron number from TM = Fe, Co to Ni the easy axis changes from the film normal to the film plane. The maximum perpendicular anisotropy reaches 0.4〜0.8 erg/cm2 for TM = Fe, Co, which is one order of magnitude higher than the magnetocrystalline anisotropy of bulk bcp Co. The dependence of the MSA on the valence electron number of TM has been successfully explained by considering the electronic states of TM combined with SiO_2 at the interface. 3. MSA in TM/ nonmagnetic oxide granular films It is found that Fe/SiO_2 granular films (Fe particle size 5〜30 nm) exhibit very high coercibity of Hc〜500 Oe which is much higher than the anisotropy field (〜100 Oe) of bulk bccFe. By considering the measured MSA of 0.4 erg/cm^2 for Fe/SiO_2 we have quantitatively explained their large Hc and the particle size dependence. This result indicates that MSA effectively enhances the magnetic anisotropy of nanoparticles embedded in granular films. 4. MSA in TM nanoparticles We have prepared isolated TM (Fe, Co, Ni) nanopartides with the diameter of D = 5〜30 nm and determined their magnetic anisotropy by the newly developed anisotropy measurement method. It is found that all the nanoparticles exhibit strong uniaxial magnetic anisotropy compared with that of bulk materials. Such anisotropy enhanoement is mainly due to the surface effect. From the micromagnetic calculations and experiments, we have confirmed that the magnetic behaviors of the nanopartivles perfectly follows the coherent rotation (Stoner Wohlfarth) model when the particle diameter Dis less than 15 nm. All the results mentioned above indicate that magnetic surface anisotropy significantly enhanoes the effective magnetic anisotropy of nanopartocles even when the bulk anisotropy is quite small. Such nanoparticles with large surface anisotropy would be very promising for development of ultra high density recording media.

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