Interpolation Theory of Ferromagnetic Heisenberg Model

This is the sequel to an earlier paper which gave a complete formulation of an interpolation theory of ferromagnetism based on the Green's-function method and the simple Tyablikov decoupling scheme. Numerical calculations of the energy and specific heat have been carried out for a few simple spin-wave models, and the results are compared with those deduced from other theories. It is found in general that the performance of the interpolation theory is poor for $S=\frac{1}{2}$ but becomes better for $S=1\mathrm{}$ or higher. Also, the theory makes a large error around the critical temperature for all spins. The spin-disorder contribution to the transport coefficients of a ferromagnetic metal are studied for a parabolic model of the spin-wave spectrum, and the results are comparable qualitatively with the experiments.