Anisotropic susceptibilities of thin ferromagnetic films within many-body Green's function theory

Transverse and parallel static susceptibilities of in-plane uniaxial anisotropic ferromagnetic films are calculated within many-body Green's function theory on the basis of an Heisenberg model. The importance of collective magnetic excitations in particular in the paramagnetic regime are stressed by comparing with mean field calculations. The paper generalizes the work of Jensen et al. [1] to the multilayer case and to spins with S>1/2.