  A microscopic theory of the spin Peltier effect in a bilayer structure
comprising a paramagnetic metal (PM) and a ferromagnetic insulator (FI) based
on the nonequilibrium Green's function method is presented. Spin current and
heat current driven by temperature gradient and spin accumulation are
formulated as functions of spin susceptibilities in the PM and the FI, and are
summarized by Onsager's reciprocal relations. By using the current formulae, we
estimate heat generation and absorption at the interface driven by the
heat-current injection mediated by spins from PM into FI.
