Band Theoretical Interpretation of Neutron Diffraction Phenomena in Ferromagnetic Metals

Abstract

Although the neutron diffraction phenomena in ferromagnetic transition metals have been successfully treated in terms of the localized spin model, this may not be regarded as a proof of the unique validity of such a model. If the correlation effect of electrons is taken into consideration by a ladder approximation, the itinerant electron model is shown to be capable of accounting for the observed diffraction equally well. The complex dynamical susceptibility is calculated with simple assumptions and the space-time correlation function of spin density is obtained from it by means of the fluctuation-dissipation theorem. The cross-section for neutron scattering derived from the correlation function explains the magnetic diffuse scattering below T c , the magnetic critical scattering around T c and the paramagnetic scattering above T c . Existing data are not enough in order to discriminate between the localized and itinerant models.