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Affiliation |
Graduate School of Engineering Science Department of Mathematical Science and Electrical-Electronic-Computer Engineering Electrical and Electronic Engineering Course |
KIKUCHI Nobuaki
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Graduate School 【 display / non-display 】
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-2023.03
Tohoku University Graduate School,Division of Engineering Doctor's Course Completed
Campus Career 【 display / non-display 】
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2024.04-Now
Akita University Graduate School of Engineering Science Department of Mathematical Science and Electrical-Electronic-Computer Engineering Electrical and Electronic Engineering Course Professor
External Career 【 display / non-display 】
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2007.04-2020.10
Tohoku University Institute of Multidisciplinary Research for Advanced Materials Assistant Professor
Research Areas 【 display / non-display 】
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Nanotechnology/Materials / Thin film/surface and interfacial physical properties
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Nanotechnology/Materials / Applied condensed matter physics
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Manufacturing Technology (Mechanical Engineering, Electrical and Electronic Engineering, Chemical Engineering) / Electric and electronic materials
Research Achievements 【 display / non-display 】
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Satoshi Tomita, Nobuaki Kikuchi, Satoshi Okamoto
Japanese Journal of Applied Physics ( IOP Publishing ) 62 ( SB ) SB1010 - SB1010 2023.03
Research paper (journal)
Abstract
We study cobalt/platinum (Co/Pt) superlattices by means of ferromagnetic resonance spectroscopy in the frequency domain. The magnetization easy-axis of superlattices, which lies in a plane of the film with Co layers of 1.5 and 1.2 nm thickness, changes to the direction perpendicular to the film surface with Co layers of 0.9 and 0.6 nm thickness. As the Co layer thickness decreases from 0.9 to 0.6 nm, the Gilbert damping parameter significantly increases while the g-value is almost constant. As the Pt layer thickness decreases from 0.6 to 0.3 nm in the superlattices with 0.9 nm thick Co layers, the damping parameter slightly decreases. The present study demonstrates that the Co/Pt superlattices with 0.9 nm thick Co layers and 0.3 nm thick Pt layers are suitable for time-varying magnetic metamaterials realizing a larger magnetic permeability modulation. -
Nobuaki Kikuchi, Katsunari Sato, Satoshi Okamoto, Osamu Kitakami, Takehito Shimatsu, Hirofumi Suto
Physical Review B ( American Physical Society (APS) ) 105 ( 5 ) 054430-1 - 054430-11 2022.02 [Refereed]
Research paper (journal)
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Shingo Tamaru, Tatsuya Yamamoto, Tomoyuki Onuma, Nobuaki Kikuchi, Satoshi Okamoto
IEEJ Transactions on Fundamentals and Materials 141 ( 5 ) 295 - 300 2021.05 [Refereed]
Research paper (journal)
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Direct detection and stochastic analysis on thermally activated domain-wall depinning events in micropatterned Nd-Fe-B hot-deformed magnets
Takahiro Yomogita, Satoshi Okamoto, Nobuaki Kikuchi, Osamu Kitakami, Hossein Sepehri-Amin, Yukiko K. Takahashi, Tadakatsu Ohkubo, Kazuhiro Hono, Keiko Hioki, Atsushi Hattori
ACTA MATERIALIA ( PERGAMON-ELSEVIER SCIENCE LTD ) 201 7 - 13 2020.12
Research paper (journal)
Although the magnetization reversal process in the permanent magnets has long been studied, it has not been fully revealed. The recent progress of the computational science realizes the atomistic calculations for the thermally activated magnetization reversal process in permanent magnets. In contrast, the experimental study on the magnetization reversal has remain to be the macroscopic evaluation. In this study, Nd-Fe-B hot-deformed magnets are micropatterned, and a staircase-like magnetization curve corresponding to the elemental domain-wall depinning event at each grain boundary is successfully observed. Each elemental domain-wall depinning event fluctuates with respect to thermal activation, and the stochastic analysis based on the Neel-Arrhenius model gives the energy barrier parameters H-0 and E-0 of each depinning event, which are the intrinsic domain-wall depinning field and energy barrier height, respectively. Three types of Nd-Fe-B hot-deformed magnets with different coercivities are adopted for this stochastic analysis. As a result, E-0 exhibits very little dependence on H-0, and its slope becomes steeper for the lower-coercivity magnet. The stochastic micromagnetics simulation based on the Landau-Lifshitz-Gilbert equation for the two-grain model with various inter-grain exchange coupling reproduces the experimentally observed relationship between E-0 and H-0. Moreover, the behavior for the lower-coercivity magnet can be explained by assuming the presence of a low magnetic anisotropy layer on the grain surface. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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Nguyen Tat Trung, Mohammad Ikram Hossain, Md Iftekharul Alam, Atsushi Ando, Osamu Kitakami, Nobuaki Kikuchi, Tsuyoshi Takaoka, Yasuyuki Sainoo, Ryuichi Arafune, Tadahiro Komeda
ACS Omega ( American Chemical Society (ACS) ) 5 ( 43 ) 28108 - 28115 2020.11
Research paper (journal)
We report a precise measurement of the sensor behavior of the field effect transistor (FET) formed with the MoS2 channel when the channel part is exposed to Cl2 gas. The gas exposure and the electrical measurement of the MoS2 FET were executed with in situ ultrahigh-vacuum (UHV) conditions in which the surface analysis techniques were equipped. This makes it possible to detect how much sensitivity the MoS2 FET can provide and understand the surface properties. With the Cl2 gas exposure to the channel, the plot of the drain current versus the gate voltage (Id-Vg curve) shifts monotonically toward the positive direction of Vg, suggesting that the adsorbate acts as an electron acceptor. The Id-Vg shifts are numerically estimated by measuring the onset of Id (threshold voltage, Vth) and the mobility as a function of the dosing amounts of the Cl2 gas. The behaviors of both the Vth shift and the mobility with the Cl2 dosing amount can be fitted with the Langmuir adsorption kinetics, which is typically seen in the uptake curve of molecule adsorption onto well-defined surfaces. This can be accounted for by a model where an impinging molecule occupies an empty site with a certain probability, and each adsorbate receives a certain amount of negative charge from the MoS2 surface up to the monolayer coverage. The charge transfer makes the Vth shifts. In addition, the mobility is reduced by the enhancement of the Coulomb scattering for the electron flow in the MoS2 channel by the accumulated charge. From the thermal desorption spectroscopy (TDS) measurement and density functional theory (DFT) calculations, we concluded that the adsorbate that is responsible for the change of the FET property is the Cl atom that is dissociated from the Cl2 molecule. The monotonic shift of Vth with the coverage suggests that the MoS2 device sensor has a good sensitivity to detect 10-3 monolayers (ML) of adsorption corresponding to the ppb level sensor with an activation time of 1 s.
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Microwave Assisted Magnetization Switching
15 ( 2 ) 89 - 95 2020.04
Introduction and explanation (scientific journal)
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First-order Reversal Curve (FORC) Analysis and Its Application for Permanent Magnet Materials
Okamoto S., Yomogita T., Miyazawa K., Kikuchi N., Kitakami O., Watanabe N., Suita N.
Materia Japan ( The Japan Institute of Metals and Materials ) 56 ( 9 ) 533 - 540 2017
Introduction and explanation (others)
1521
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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
Research paper (international conference proceedings)
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Tuning Magnetic Anisotropy and Curie Temperature of L1<SUB>0</SUB>-FePt Granular films
T. Shimatsu, T. Ono, T. Moriya, H. Nakata, K. Komiyama, S. Uchida, H. Oyama, H. Kikuchi, H. Kataoka, K. Sato, A. Furuta, T. Yoshizawa, M. Hatayama, K. Tsumura, N. Kikuchi, O. Kitakami
Digest of the 28th Magnetic Recording Conference 2017(TMRC2017) 2017.08 [Invited]
Research paper (international conference proceedings)
Tsukuba, August(2017) A-1
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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
Research paper (university bulletin, research institution)
562
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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
Research paper (university bulletin, research institution)
560
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Permeability control for time-varying metamaterials
MAG22146 2022.11
Summary of the papers read (national conference and other science council)
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Effect of thermal fluctuations on microwave assisted switching in Co/Pt nanodot array
45 ( 14 ) 7 - 11 2021.06
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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 - 32 2020.12
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2019 ( 197 ) 13 - 17 2019.12
◆Original paper【 display / non-display 】
◆Introduction and explanation【 display / non-display 】
◆International conference proceedings【 display / non-display 】
◆University bulletin, Research institution【 display / non-display 】
◆Other【 display / non-display 】
Grant-in-Aid for Scientific Research 【 display / non-display 】
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Research of synthetic antiferromagnet for THz devices with Brillouin light scattering
Grant-in-Aid for Scientific Research(B)
Project Year： 2021.04 - 2024.03
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Energy loss analysis in soft magnetic particles for high frequency region and development of its design method
Grant-in-Aid for Scientific Research(B)
Project Year： 2020.04 - 2023.03 Investigator(s): Satoshi Okamoto
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Feasibility study on multilevel memory based on skyrmion dynamics
Grant-in-Aid for Challenging Research (Exploratory)
Project Year： 2017.06 - 2019.03 Investigator(s): Okamoto Satoshi, Sato Rie
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Generation of circularly polarized femtosecond coherent soft x-rays and its application to ultrafast spin dynamics
Grant-in-Aid for Scientific Research(A)
Project Year： 2017.04 - 2021.03 Investigator(s): Takahashi Eiji
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Engineering technology for high frequency spin dynamics
Grant-in-Aid for Scientific Research(B)
Project Year： 2017.04 - 2020.03 Investigator(s): Okamoto Satoshi
Presentations 【 display / non-display 】
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Analysis on Iron Loss of Sendust Dust Cores based on Magnetization Reversal Processes
N. Ono, Y. Uehara, Y. Endo, S. Yoshida, N. Kikuchi, S. Okamoto
INTERMAG 202 2023.05 - 2023.05
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Effect of film thickness on microwave assisted switching behavior
N. Kikuchi, K. Sato, M. Hatayama, T. Shimatsu, S. Okamoto
INTERMAG 2023 2023.05 - 2023.05
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Permeability Control of Ferromagnetic Wires for Time- varying Spintronic Metamaterials
T. Kodama, N. Kikuchi, S. Okamoto, S. Ohno, S. Tomita
INTERMAG 2023 2023.05 - 2023.05
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Spin-current Driven Magnetic Meta-atoms for Time- Varying Permeability
R. Shimizu, T. Kodama, N. Kikuchi, S. Okamoto, S. Ohno, S. Tomita
INTERMAG 2023 2023.05 - 2023.05
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Visualization of the magnetization reversal processes in He jet-milled Nd-Fe-B sintered magnet by X-ray magnetic tomography
2020.12 - 2020.12