Single-Site Functional-Integral Approach to Itinerant-Electron Ferromagnetism

Abstract

Itinerant-electron ferromagnetism at finite temperatures is discussed by using the functional-integral method with two fields within the static and saddle-point approximations combined with the single-site approximation; a single atom of a pure metal is regarded as an impurity embedded in the host which is treated by a kind of the alloy-analogy approximation. The amplitude of the local magnetic moment is shown to have a weak temperature dependence and to remain finite even in the paramagnetic state, where the spin susceptibility obeys an approximate Curie-Weiss law. Numerical calculations are made with the use of a simplified model for the density of states of bcc transition metals. Calculated results are discussed with reference to experimental data of iron.