  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.
