Effect of Spin Fluctuations on Itinerant Electron Ferromagnetism

Abstract

The effect of electron correlation on itinerant electron ferromagnetism, or the correction to the Stoner (Hartree-Fock) theory, is studied. The additional free energy (correction to the Hartree-Fock contribution) as a function of magnetization is expressed exactly in terms of the transversal spin fluctuations or the transversal dynamical susceptibilities and is actually calculated by using a modified random phase approximation for the dynamical susceptibilities. This contribution turns out to be predominant in describing the thermodynamical properties of itinerant ferromagnets, leading to serious modification of the Stoner theory; the Curie temperature is lowered and the magnetic susceptibility shows approximate Curie-Weiss behavior.