LANDAU-LIFSHITZ EQUATION IN ITINERANT ELECTRON FERROMAGNETS

The Landau-Lifshitz equation is the basic equation governing the time evolution of long-wavelength disturbances in ferromagnets. We report here a new microscopic derivation of this equation, valid for itinerant electron ferromagnets. The derivation is valid for the nonlinear case in which the spin fluctuates over a large angular range globally. In particular it includes the time dependence of magnetization fluctuations above the Curie temperature. We also find the generalization of the Landau-Lifshitz equation needed when the magnetization magnitude is not spatially uniform.