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arXiv · 2210.03346

Composition-tunable magnon-polaron anomalies in spin Seebeck effects in epitaxial Bi$_x$Y$_{3-x}$Fe$_{5}$O$_{12}$ films

Takashi Kikkawa·Koichi Oyanagi·Tomosato Hioki·Masahiko Ishida·Zhiyong Qiu·Rafael Ramos·Yusuke Hashimoto·Eiji Saitoh
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Abstract

We have investigated hybridized magnon-phonon excitation (magnon polarons) in spin Seebeck effects (SSEs) in Bi$_x$Y$_{3-x}$Fe$_{5}$O$_{12}$ (Bi$_x$Y$_{3-x}$IG; $x=0$, $0.5$, and $0.9$) films with Pt contact. We observed sharp peak structures in the magnetic field $H$ dependence of the longitudinal SSE (LSSE) voltages, which appear when the phonon dispersions are tangential to the magnon dispersion curve in Bi$_x$Y$_{3-x}$IG. By increasing the Bi amount $x$, the peak fields in the LSSE shift toward lower $H$ values due to the reduction of the sound velocities in Bi$_x$Y$_{3-x}$IG. We also measured the SSE in a nonlocal configuration and found that magnon-polaron anomalies appear with different signs and intensities. Our result shows composition-tunability of magnon-polaron anomalies and provides a clue to further unravel the physics of magnon-polaron SSEs.

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Takashi Kikkawa, Koichi Oyanagi, Tomosato Hioki, Masahiko Ishida, Zhiyong Qiu, Rafael Ramos, Yusuke Hashimoto, Eiji Saitoh. 2022-10-07. Composition-tunable magnon-polaron anomalies in spin Seebeck effects in epitaxial Bi$_x$Y$_{3-x}$Fe$_{5}$O$_{12}$ films. https://doi.org/10.1103/physrevmaterials.6.104402

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