Calculations of the dynamic susceptibility of nickel and iron

The spin dynamics of the transition-metal ferromagnets nickel and iron are investigated within the framework of the itinerant theory of magnetism. The theory is developed in terms of a generalized random-phase approximation which incorporates the band and wave-vector dependence of relevant interaction matrix elements. In contrast to constant-matrix-element approximations, this formalism generates band- and wave-vector-dependent splitting of the energy bands, possible "optical" spin-wave modes, and a different interpretation of the spin-wave disappearance phenomena. First-principles numerical calculations of the neutron scattering intensity based on this model have been found to be in excellent agreement with experiments. Recent neutron scattering experiments have also verified the existence of an "optical" spin-wave branch predicted by this theory.