  The spin Seebeck effect refers to the generation of a spin voltage caused by
a temperature gradient in a ferromagnet, which enables the thermal injection of
spin currents from the ferromagnet into an attached nonmagnetic metal over a
macroscopic scale of several millimeters. The inverse spin Hall effect converts
the injected spin current into a transverse charge voltage, thereby producing
electromotive force as in the conventional charge Seebeck device. Recent
theoretical and experimental efforts have shown that the magnon and phonon
degrees of freedom play crucial roles in the spin Seebeck effect. In this
article, we present the theoretical basis for understanding the spin Seebeck
effect and briefly discuss other thermal spin effects.
