Thermal properties of magnons and the spin Seebeck effect in yttrium iron garnet/normal metal hybrid structures

In the study of the spin Seebeck effect (SSE) in structures with a ferromagnetic insulator (FMI) in contact with a normal metal it is important to know the distributions of the temperatures of the magnon, phonon, and electron systems. Studies of the SSE in yttrium iron garnet (YIG) have relied on the thermal properties of magnons in YIG calculated with expressions valid for low temperatures. Here we present a calculation of the magnon specific heat and thermal conductivity in YIG and show that the values at room temperature are very discrepant from numbers used in the literature. With our values we calculate the temperature profiles of the magnon and phonon systems in a FMI subject to a temperature gradient in the configurations used to study the transverse and longitudinal SSE. In both cases the results are quite different from those obtained in previous studies.