Details of the Researcher

PHOTO

Koujiro Hoshi
Section
Advanced Institute for Materials Research
Job title
Specially Appointed Assistant Professor(Research)

Research History 2

  • 2026/01 - Present
    東北大学材料科学高等研究所

  • 2021/04 - 2025/12
    The University of Tokyo　The Graduate School of Engineering Department of Applied Physics

Professional Memberships 2

  • 応用物理学会

    2025/05 -

  • 日本物理学会

    2016/09 -

Research Interests 1

  • spintronics

Research Areas 1

  • Natural sciences / Magnetism, superconductivity, and strongly correlated systems /

Papers 12

  1. Single- and two-mode magnon thermal squeezing

    Tomosato Hioki, Kaito Tojo, Mehrdad Elyasi, Sohei Horibe, Hiroki Shimizu, Koujiro Hoshi, Takahiko Makiuchi, Gerrit E. W. Bauer, Eiji Saitoh

    Nature Physics　2026/06/01

    Publisher: Springer Science and Business Media LLC

    DOI： 10.1038/s41567-026-03294-4 　

    ISSN： 1745-2473

    eISSN： 1745-2481

  2. High harmonic generation by dynamic Fermi surface nesting Peer-reviewed

    Koujiro Hoshi, Terufumi Yamaguchi, Tomosato Hioki, Eiji Saitoh

    Physical Review B　113　(9)　2026/03/09

    Publisher: American Physical Society (APS)

    DOI： 10.1103/wjf4-1zyj 　

    ISSN： 2469-9950

    eISSN： 2469-9969

  3. Electric voltage generation by standing spin waves in a ferromagnetic metal

    Koujiro Hoshi, Tomosato Hioki, Eiji Saitoh

    Physical Review Applied　21　(6)　2024/06/25

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevapplied.21.064057 　

    eISSN： 2331-7019

  4. Topological spin Hall effect in antiferromagnets driven by vector Néel chirality Peer-reviewed

    Kazuki Nakazawa, Koujiro Hoshi, Jotaro J. Nakane, Jun-ichiro Ohe, Hiroshi Kohno

    Physical Review B　109　(24)　2024/06/06

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevb.109.l241105 　

    ISSN： 2469-9950

    eISSN： 2469-9969

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    Spin Hall effect of spin-texture origin is explored theoretically for antiferromagnetic (AF) metals. It is found that a vector chirality formed by the Néel vector gives rise to a topological spin Hall effect. This is topological since it is proportional to the winding number counted by in-plane vector chirality along the sample edge, which can be nonvanishing for AF merons but not for AF skyrmions. The effect is enhanced when the Fermi level lies near the AF gap, and, surprisingly, at weak coupling with small AF gap. These features are confirmed numerically based on the Landauer-Büttiker formula. Important roles played by nonadiabatic processes and spin dephasing are pointed out.

  5. Persistent magnetic coherence in magnets

    Takahiko Makiuchi, T. Hioki, Hiroki Shimizu, K. Hoshi, Mehrdad Elyasi, Kei Yamamoto, Naoto Yokoi, Alexander A. Serga, Burkard Hillebrands, Gerrit Bauer, Eiji Saitoh

    Nature Materials　2024/02/06

    Publisher: Springer Science and Business Media LLC

    DOI： 10.1038/s41563-024-01798-z 　

    ISSN： 1476-4660

  6. Electrical detection of parallel parametric amplification and attenuation in a Y3Fe5O12/Pt bilayer disk

    Geil Emdi, Tomosato HIOKI, Koujiro Hoshi, Eiji Saitoh

    Physical Review B　108　(14)　2023/10/26

    Publisher: American Physical Society ({APS})

    DOI： 10.1103/physrevb.108.l140410 　

    ISSN： 2469-9950 2469-9969

  7. Switching of magnon parametric oscillation by magnetic field direction

    Sohei Horibe, Hiroki Shimizu, Koujiro Hoshi, Takahiko Makiuchi, Tomosato HIOKI, Eiji Saitoh

    Applied Physics Express　16　(7)　073001-073001　2023/07/01

    Publisher: {IOP} Publishing

    DOI： 10.35848/1882-0786/acdfb8 　

    ISSN： 1882-0778 1882-0786

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    <jats:title>Abstract</jats:title> <jats:p>Parametric oscillation occurs when the resonance frequency of an oscillator is periodically modulated. Owing to time-reversal symmetry breaking in magnets, nonreciprocal magnons can be parametrically excited when spatial-inversion symmetry breaking is provided. This means that magnons with opposite propagation directions have different amplitudes. Here we demonstrate switching on and off the magnon parametric oscillation by reversing the external field direction applied to a Y<jats:sub>3</jats:sub>Fe<jats:sub>5</jats:sub>O<jats:sub>12</jats:sub> micro-structured film. The result originates from the nonreciprocity of surface mode magnons, leading to field-direction dependence of the magnon accumulation under nonuniform microwave pumping. Our numerical calculation well reproduces the experimental result.</jats:p>

  8. Spin motive force induced by parametric excitation

    Koujiro Hoshi, Tomosato HIOKI, Eiji Saitoh

    Applied Physics Letters　121　(21)　212404-212404　2022/11/21

    Publisher: {AIP} Publishing

    DOI： 10.1063/5.0129466 　

    ISSN： 0003-6951 1077-3118

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    <jats:p> Spin motive force generated by parametrically excited magnetization dynamics is numerically investigated. We calculate spin motive force in a permalloy disk under an ac magnetic field with twice the ferromagnetic resonance frequency parallel to the static magnetic field based on the Landau–Lifshitz–Gilbert equation. We found that large spin motive force originating from standing spin waves driven by parametric excitation appears in the system. The observed time dependence of the voltage shows a dc voltage with an ac component oscillating with twice of the resonance frequency. The estimated amplitude of the voltage due to the spin motive force is [Formula: see text]. We also investigate spin motive force driven by different modes of standing spin waves. Our numerical results extend the way to generate spin motive force by making use of the magnetization dynamics with the steep spatial modulation created by nonlinear spin waves excitation, without a non-uniform magnetization structure such as a conventional magnetic domain wall and a vortex. </jats:p>

  9. Real-space observation of standing spin-wave modes in a magnetic disk

    Tomosato HIOKI, Tomonao Araki, Kosuke Umemura, Koujiro Hoshi, Eiji Saitoh

    Applied Physics Letters　121　(13)　132402-132402　2022/09/26

    Publisher: {AIP} Publishing

    DOI： 10.1063/5.0098772 　

    ISSN： 0003-6951 1077-3118

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    <jats:p> In-plane standing spin-wave modes in a minute magnetic disk are directly observed by using time-resolved magneto-optical microscopy synchronized with microwaves. The time-resolved microscopy allowed us to obtain snapshots of standing spin-wave modes in a magnetic disk, which show a hourglass-like standing spin wave pattern. We found that the characteristic pattern is caused by spatially nonuniform magnetization and a strong microwave excitation in terms of finite element calculation and micromagnetic simulations. The technique we developed in this work allows us to access magnetization dynamics in microstructured magnets under strong microwave pumping. </jats:p>

  10. Coupled-oscillator collective mode of a magnetic chiral soliton lattice

    Koujiro Hoshi, Jun-ichiro Kishine, Jun-ichiro Ohe

    Physical Review B　102　(13)　2020/10/12

    Publisher: American Physical Society ({APS})

    DOI： 10.1103/physrevb.102.134414 　

    ISSN： 2469-9950 2469-9969

  11. Magnon-drag thermoelectric transport with skyrmion structure

    Koujiro Hoshi, Terufumi Yamaguchi, Akihito Takeuchi, Hiroshi Kohno, Jun-ichiro Ohe

    Applied Physics Letters　117　(6)　062404-062404　2020/08/10

    Publisher: {AIP} Publishing

    DOI： 10.1063/5.0017272 　

    ISSN： 0003-6951 1077-3118

  12. Chirality-induced spin current through spiral magnets

    Hiroki Watanabe, Koujiro Hoshi, Jun-ichiro Ohe

    Physical Review B　94　(12)　2016/09/23

    Publisher: American Physical Society ({APS})

    DOI： 10.1103/physrevb.94.125143 　

    ISSN： 2469-9950 2469-9969

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Misc. 1

  1. Theoretical study on magnon-drag effect Invited Peer-reviewed

    Magnetics Japan　16　(6)　305-311　2021/12