Temperature-switched anomaly in the spin Seebeck effect in Gd3Fe5O12

The magnon-polaron induced anomaly has recently been observed in the magnetic field dependence of the spin seebeck effect in Y3Fe5O12 [T. Kikkawa et al., Phys. Rev. Lett. 117,207203 (2016)]. In the present theoretical work, we show that such an anomaly in Gd3Fe5O12 depends strongly on the temperature, and it exists only at high temperature but disappears at low temperature. The finite-temperature magnon-polaron anomaly results from the distortion of the magnon dispersion driven by thermal magnon excitation. In contrast to the scenario in Y3Fe5O12, the anomaly in Gd3Fe5O12 can present either single-peak or double-peak features at different temperatures.