  We calculate the phonon, electron and magnon temperature profiles in yttrium
iron garnet/platinum bilayers by diffusive theory with appropriate boundary
conditions, in particular taking into account interfacial thermal resistances.
Our calculations show that in thin film hybrids, the interface magnetic heat
conductance qualitatively affects the magnon temperature. Based on published
material parameters we assess the degree of non-equilibrium at the yttrium iron
garnet/platinum interface. The magnitude of the spin Seebeck effect derived
from this approach compares well with experimental results for the longitudinal
spin Seebeck effect. Additionally we address the temperature profiles in the
transverse spin Seebeck effect.
