Hideo Hasegawa

TL;DR: In this paper, a functional-integral method with two fields within the static and saddle-point approximations combined with the single-site approximation was used to analyze the ferromagnetic properties of bcc transition metals.

TL;DR: 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 as discussed by the authors, which is shown to provide an interpolating description of 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.

TL;DR: In this paper, a spin-fluctuation theory was applied to iron and nickel for a discussion of their magnetic and thermodynamical properties at finite temperatures with a slight extension including the effect of charge fields within the steepest-descent approximation.

TL;DR: In this article, a unified description for magnetism of narrow band electron systems on the basis of a functional integral formalism within the static approximation is given, and the free energy functional from a given band structure and its closed form expression is given for arbitrary amplitudes of the spin and charge density fluctuations, correponding to arbitrary strength of the electron-electron interaction.

TL;DR: In this paper, the specific heat of nearly and weakly antiferromagnetic metals is discussed by using the renormalized spin fluctuation theory, which has been previously applied to the study of the effect of spin fluctuations on the magnetic susceptibility.