Nii, Yoichi

写真a

Affiliation

Faculty of Science and Technology, Department of Applied Physics and Physico-Informatics (Yagami)

Position

Associate Professor
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Career 【 Display / hide 】

  • 2012.04
    -
    2013.03

    The University of Tokyo, 大学院新領域研究科, 日本学術振興会 特別研究員(PD)

  • 2013.04
    -
    2015.06

    理化学研究所, 創発物性科学研究センター, 特別研究員

  • 2015.07
    -
    2018.06

    The University of Tokyo, Graduate School of Arts and Sciences, 助教

  • 2018.07
    -
    2022.06

    Tohoku university, Institute of Materials Research, Assistant professor

  • 2019.10
    -
    2023.03

    科学技術振興機構, さきがけ研究員（兼任）

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Academic Degrees 【 Display / hide 】

  • 博士（理学）, Tohoku University, 2012.03

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Research Areas 【 Display / hide 】

  • Natural Science / Semiconductors, optical properties of condensed matter and atomic physics

  • Natural Science / Magnetism, superconductivity and strongly correlated systems

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Research Keywords 【 Display / hide 】

  • トポロジカル磁気構造

  • Nano device

  • Acoustics

  • マイクロ波光学

  • Scanning Microwave Impedance Microscopy

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Papers 【 Display / hide 】

  • Current-Induced Sliding Motion in a Helimagnet MnAu2

    Yuta Kimoto, Hidetoshi Masuda, Takeshi Seki, Yoichi Nii, Jun-ichiro Ohe, Yusuke Nambu, Yoshinori Onose

    Physical Review Letters (American Physical Society (APS))  134 ( 5 )  2025.02

    ISSN  0031-9007

    　View Summary

    We found signatures of current-induced sliding motion in helimagnetic MnAu2 thin films. An abrupt change in differential resistivity occurred at a threshold bias current in the helimagnetic state, whereas it was absent in the induced ferromagnetic state. Broadband voltage noise also emerged above the threshold current in the helimagnetic state. Based on the similarity to canonical charge and spin density wave systems, we ascribed the origin of these phenomena to the sliding motion of the helimagnetic structure.

    Published by the American Physical Society 2025

  • Band asymmetry-driven nonreciprocal electronic transport in a helimagnetic semimetal a-EuP3

    Alex Hiro Mayo, Darius-Alexandru Deaconu, Hidetoshi Masuda, Yoichi Nii, Hidefumi Takahashi, Rodion Vladimirovich Belosludov, Shintaro Ishiwata, Mohammad Saeed Bahramy, Yoshinori Onose

    Proceedings of the National Academy of Sciences  ( 122(4) ) e2405839122 2025.01

    Research paper (scientific journal), Joint Work, Accepted

  • Observation of Nonreciprocal Diffraction of Surface Acoustic Wave

    Y. Nii, K. Yamamoto, M. Kanno, S. Maekawa, Y. Onose

    Physical Review Letters (American Physical Society (APS))  134 ( 2 )  2025.01

    Lead author, Corresponding author, Accepted,  ISSN  0031-9007

    　View Summary

    Rectification phenomenon caused by the simultaneous breaking of time reversal
    and spatial inversion symmetries has been extended to a wide range of
    (quasi)particles and waves; however, the nonreciprocal diffraction, which is
    the imbalance of upward and downward deflections, was previously observed only
    for photons and remained to be extended to other (quasi)particles. In this
    study, we present evidence of the nonreciprocal diffraction of surface acoustic
    wave (SAW) utilizing a magnetoelastic grating on a SAW device. Asymmetric
    diffraction intensities were observed when the ferromagnetic resonance was
    acoustically excited. Based on a theoretical model, we attribute the
    microscopic origin of this phenomenon to the resonant scattering involving
    ferromagnetic resonance excitations. The novel property may pave an avenue to
    further development of SAW devices for various purposes, including microwave
    communications and quantum engineering applications.

  • A high-temperature multiferroic Tb2(MoO4)3

    Shimon Tajima, Hidetoshi Masuda, Yoichi Nii, Shojiro Kimura, Yoshinori Onose

    Communications Materials (Springer Science and Business Media LLC)  5 ( 1 )  2024.12

    　View Summary

    Abstract

    Magnetoelectric mutual control in multiferroics, which is the electric control of magnetization, or reciprocally the magnetic control of polarization has attracted much attention because of its possible applications to spintronic devices, multi-bit memories, and so on. While the required working temperature for the practical application is much higher than room temperature, which ensures stable functionality at room temperature, the reported working temperatures were at most around room temperature. Here, we demonstrated magnetic control of ferroelectric polarization at 432 K in ferroelectric and ferroelastic Tb<sub>2</sub>(MoO<sub>4</sub>)<sub>3</sub>, in which the polarity of ferroelectric polarization is coupled to the orthorhombic strain below the transition temperature 432 K. The paramagnetic but strongly magnetoelastic Tb<sup>3+</sup> magnetic moments enable the magnetic control of ferroelectric and ferroelastic domains; the ferroelectric polarization is controlled depending on whether the magnetic field is applied along [110] or [1$$\bar{1}$$0]. This result may pave a new avenue for designing high-temperature multiferroics.

  • Microscopic evaluation of spin and orbital moment in ferromagnetic resonance

    Yuta Ishii, Yuichi Yamasaki, Yusuke Kozuka, Jana Lustikova, Yoichi Nii, Yoshinori Onose, Yuichi Yokoyama, Masaichiro Mizumaki, Jun-ichi Adachi, Hironori Nakao, Taka-hisa Arima, Yusuke Wakabayashi

    Scientific Reports (Springer Science and Business Media LLC)  14 ( 1 )  2024.07

    　View Summary

    Abstract

    Time-resolved X-ray magnetic circular dichroism under the effects of ferromagnetic resonance (FMR), known as X-ray ferromagnetic resonance (XFMR) measurements, enables direct detection of precession dynamics of magnetic moment. Here we demonstrated XFMR measurements and Bayesian analyses as a quantitative probe for the precession of spin and orbital magnetic moments under the FMR effect. Magnetization precessions in two different Pt/Ni-Fe thin film samples were directly detected. Furthermore, the ratio of dynamical spin and orbital magnetic moments was evaluated quantitatively by Bayesian analyses for XFMR energy spectra around the Ni $$L_{2,3}$$ absorption edges. Our study paves the way for a microscopic investigation of the contribution of the orbital magnetic moment to magnetization dynamics.

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Reviews, Commentaries, etc. 【 Display / hide 】

  • Magnetoelastic study on the itinerant helimagnet SrFeO<sub>3</sub> and reconsideration of the phase diagram

    厳正輝, 今城周作, 鬼頭俊介, 徳永祐介, 新居陽一, 池田暁彦, 小濱芳允, 金道浩一, 石渡晋太郎, 有馬孝尚, 有馬孝尚

    日本物理学会講演概要集(CD-ROM) 79 ( 1 )  2024

    ISSN  2189-079X

  • Observation of phonon dispersion at low temperature phases in FeV<sub>2</sub>O<sub>4</sub> using synchrotron X-ray inelastic scattering

    萬條太駿, 鬼頭俊介, 片山尚幸, 中村真一, 勝藤拓郎, 新居陽一, 新居陽一, 有馬孝尚, 有馬孝尚, 長谷川巧, 石川大介, 石川大介, BARON A. Q. R., BARON A. Q. R., 澤博

    日本物理学会講演概要集(CD-ROM) 76 ( 2 )  2021

    ISSN  2189-079X

  • Direct observation of valence electron density distribution in AV2O4(A = Fe,Mn) using core differential Fourier synthesis method

    萬條太駿, 鬼頭俊介, 片山尚幸, 新居陽一, 有馬孝尚, 有馬孝尚, 勝藤拓郎, 勝藤拓郎, 澤博

    日本物理学会講演概要集(CD-ROM) 75 ( 1 )  2020

    ISSN  2189-079X

  • Observation of 3d orbital state in spinel oxide FeV<sub>2</sub>,O<sub>4</sub> with Fe and V having orbital degree of freedom

    萬條太駿, 鬼頭俊介, 片山尚幸, 野村悠祐, 有田亮太郎, 有田亮太郎, 新居陽一, 新居陽一, 有馬孝尚, 有馬孝尚, 澤博

    日本物理学会講演概要集(CD-ROM) 75 ( 2 )  2020

    ISSN  2189-079X

  • コア差フーリエ合成解析によるFeV<sub>2</sub>O<sub>4</sub>の軌道秩序の観測 II

    萬條太駿, 鬼頭俊介, 片山尚幸, 新居陽一, 有馬孝尚, 澤博

    日本物理学会講演概要集(CD-ROM) 74 ( 1 )  2019

    ISSN  2189-079X

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Research Projects of Competitive Funds, etc. 【 Display / hide 】

  • 対称性の破れた絶縁体における新しい変位電流応答の開拓

    2024.06
    -
    2026.03

    挑戦的研究(萌芽), Research grant, Principal investigator

  • 超低損失なGHzトポロジカルフォノニックデバイスの創出

    2024.04
    -
    2027.03

    日本学術振興会 科学研究費助成事業 基盤研究(B), Principal investigator

  • 先端計測による強相関フォノニクスと熱機能の開拓

    2023.04
    -
    2030.03

    創発的研究支援事業, Principal investigator

  • 非線形マイクロ波顕微鏡の開発と対称性の破れのナノスケールイメージング

    2022.07
    -
    2023.06

    村田学術振興財団, Principal investigator

  • Exploration of novel material functions utilizing angular momentum conversion in symmetry-broken magnets

    2021.04
    -
    2024.03

    Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (B), No Setting

    　View Summary

    本年度は、まずスピン角運動量が120度磁気構造を示す遍歴磁性体PdCrO2において非相反伝導の観測を行った。集束イオンビーム加工によって電流密度を増強し、非線形応答である非相反伝導の観測に成功した。詳細な磁場角度依存性の測定を行い、対称性の観点から実験結果を基に磁気構造に関する考察し、中性子散乱実験から同定された可能な磁気構造の中から最も実現している可能性が高いものを同定した。また、電気四重極子の長距離秩序を示すフラストレート系のTb2Ti2O7において磁気モーメント（スピンおよび軌道角運動量）と電気四重極子の結合から生じる巨大な磁気弾性応答（音速や歪の磁場変化）を明らかにした。 まず、四重極秩序に伴う音速の異常を観測し、より高温における磁気弾性応答についても詳細な磁場角度依存性を基にした解析を行い、転移温度よりも十分高い10K程度まで四重極子間の相関が存在することを明らかにした。さらには、圧電基板上にすだれ状電極のペアと強磁性Niを作製して表面弾性波と強磁性が結合したデバイスを作製し、表面弾性波の角運動量を用いて強磁性体の磁化を制御することに成功し、キラル磁性体MnSiのフォノンスペクトルをX線非弾性散乱によって測定することにより空間反転対称性の破れによるフォノン角運動量に関する分裂を明らかにした。以上の論文発表された成果に加えて、角運動量変換の新現象であるキラル磁性体における磁気共鳴誘起の起電力や空間反転対称性が破れた磁性体における熱流誘起の磁化制御の観測を目指した研究を進行している。

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Awards 【 Display / hide 】

  • 文部科学大臣表彰 若手科学者賞

    2024.04

  • 第140回金研講演会 優秀ポスター賞

    新居陽一, 廣金優二, 是常隆, 石川大介, Alfred Q. R. Baron, 小野瀬佳文, 2021.05, 東北大学金属材料研究所, キラル磁性体MnSi のフォノン分散に及ぼす対称性の破れの効果

  • Best poster awards in Summit of Materials Science conference

    Yoichi Nii, 2018.10, Institute for Materials Research, Tohoku university

  • JPSJ Editor's Choice, Microwave Magnetochiral Effect in the Non-centrosymmetric Magnet CuB2O4

    Yoichi Nii, Ryo Sasaki, Yusuke Iguchi, Yoshinori Onose, 2017.01, Journal of the Physical Society of Japan

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Courses Taught 【 Display / hide 】

  • PRESENTATION TECHNIQUE

    2025

  • LABORATORY IN SCIENCE

    2025

  • INDEPENDENT STUDY ON FUNDAMENTAL SCIENCE AND TECHNOLOGY

    2025

  • GRADUATE RESEARCH ON FUNDAMENTAL SCIENCE AND TECHNOLOGY 2

    2025

  • GRADUATE RESEARCH ON FUNDAMENTAL SCIENCE AND TECHNOLOGY 1

    2025

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