Inelastic neutron scattering study of magnon excitation by ultrasound injection in yttrium iron garnet

The magnon excitation by ultrasound injection in Y3Fe5O12 is studied by inelastic neutron scattering. Both longitudinal and transverse ultrasound injections enhanced the inelastic neutron scattering intensity. We analyzed the nonequilibrium magnon steady state using the effective magnon temperature model. The large deviation of the effective magnon temperature from the sample temperature is observed at the ultrasound longitudinal mode along [0, 0, 1] at similar to 10 K and [1, 1, 1] at similar to 140 K. This dependence suggests that the nonequilibrium steady state can be achieved only by strong spin-lattice coupling in Y3Fe5O12. The spin-lattice coupling exhibits a decrease largely above 100 K, indicating that it could be the main origin of the degradation of longitudinal spin Seebeck effect at the temperature range.