Composition-tunable magnon-polaron anomalies in spin Seebeck effects in epitaxial BixY3-xFe5O12 films

We have investigated hybridized magnon-phonon excitation (magnon polarons) in spin Seebeck effects (SSEs) in BixY3-xFe5O12 (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.