Spin fluctuation theory of ferromagnetic metals

Ferromagnetic metals at finite temperatures are discussed using the functional integral method along the lines of the unifield spin fluctuation theory of Moriya and Takahashi. We develop a simple approach which makes use of only the density of states but still takes account of the nonlocal nature of the spin fluctuations with the aid of a single-site coherent potential approximation. The effect of the charge density fluctuation is also taken into account within the saddle point approximation. The results of numerical calculations for various model densities of states including those for bcc and fcc d-metals are presented. Particularly, the Curie temperatures and the Curie-Weiss magnetic susceptibilities for Fe, Co and Ni seem to be fairly well reproduced.