Temperature-switched anomaly in the spin Seebeck effect in Gd3Fe5O12

Abstract

The magnon-polaron induced anomaly has recently been observed in the magnetic field dependence of the spin seebeck effect in ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ [T. Kikkawa et al., Phys. Rev. Lett. 117, 207203 (2016)]. In the present theoretical work, we show that such an anomaly in ${\mathrm{Gd}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ 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 ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$, the anomaly in ${\mathrm{Gd}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ can present either single-peak or double-peak features at different temperatures.