arXiv subjects

Koujiro Hoshi

Publications and source records attributed to Koujiro Hoshi.

4 recordsLinked to original sources

arXiv2026

Double anticrossings induced by nonlinear magnon interactions

We observe pump-induced double anticrossings whose gap sizes and center-frequency shifts depend strongly on pump power, indicating a nonlinear mechanism. The anticrossings vanish at high magnetic fields, where energy conservation suppresses three-magnon splitting, thereby identifying the underlying process as three-magnon scattering. We attribute the double anticrossings to nondegenerate three-magnon splitting, which generates two magnon populations at distinct frequencies. Each population forms a standing-wave mode and couples independently to the Kittel mode, giving rise to two effective coupling channels. These results demonstrate that nonlinear magnon interactions can dynamically generate multiple coupling channels within a single system.

cond-mat.mes-hall↗

arXiv2023

Electrical detection of parallel parametric amplification and attenuation in $\mathrm{Y}_3\mathrm{Fe}_5\mathrm{O}_{12}$/$\mathrm{Pt}$ bilayer disk

We report a systematic quantitative evaluation of parametric amplification gain of magnetization dynamics in ytirrium iron garnet ($\mathrm{Y}_3\mathrm{Fe}_5\mathrm{O}_{12}$) thin disk via a.c. spin pumping and inverse spin Hall effect. We demonstrate its signature phase-dependence where amplification and attenuation occur every $\fracπ{2}$ phase shift of the input signal. The results also show the pump-power dependence of the gain that is explained well by our theoretical model. Finally, the optimal conditions for the amplification is investigated by measuring the magnetic field dependence, where we find the highest gain of 11.4 dB.

physics.app-ph↗

arXiv2023

Switching of magnon parametric oscillation by magnetic field direction

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$_3$Fe$_5$O$_{12}$ micro-structured film. The result originates from the nonreciprocity of surface mode magnons, leading to field-direction dependence of the magnon accumulation under a nonuniform microwave pumping. Our numerical calculation well reproduces the experimental result.

cond-mat.mes-hall↗

arXiv2023

Topological spin Hall effect in antiferromagnets driven by vector N\'eel chirality

Spin Hall effect of spin-texture origin is explored theoretically for antiferromagnetic (AF) metals. It is found that a vector chirality formed by the N\'eel 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-B\"uttiker formula. Important roles played by nonadiabatic processes and spin dephasing are pointed out.

cond-mat.mes-hall↗