Single-Site Spin Fluctuation Theory of Itinerant-Electron Systems with Narrow Bands

Abstract

The spin fluctuation theory of itinerant-electron magnetism is developed by using the static functional integral method combined with the single-site alloy analogy approximation. The theory is shown to provide an interpolating description of itinerant electron magnetism yielding good results in some important limits; in the weak interaction limit or T=0 K it reduces to the Hartree-Fock theory, and in the strong coupling limit for the half-filled band it reproduces the results of the molecular-field theory. With the use of the half-filled Bell shape band the temperature dependences of the average moment, the local moment, the susceptibility and the specific heat are calculated numerically for various values of the electron-electron interaction.