Magnetic susceptibilities in the itinerant model: Many-band effects

Abstract

Explicit expressions for the longitudinal and transverse spin susceptibilities of an itinerant ferromagnet with many bands are derived by means of diagrammatic techniques within the random phase approximation. The Hamiltonian used is a generalization of the Hubbard one-band Hamiltonian. No approximation is made for the wavevector or band index dependence of the form factors, and both interband and intraband contributions are treated. The expression for the longitudinal component shows features, absent in the one band case, which may account for the discrepancy found by Lowde and Windsor between their experimental values for the longitudinal contribution to the neutron scattering cross section of nickel, and those calculated using (essentially) a one-band theory.