SPHERICAL MODEL FOR ANISOTROPIC FERROMAGNETIC-FILMS

The corrections to the Curie temperature T-c of a ferromagnetic film c onsisting of N layers are calculated for N >> 1 for the model of D-com ponent classical spin vectors in the limit D --> infinity, which is ex actly soluble and close to the spherical model. The present approach a ccounts, however, for the magnetic anisotropy playing the crucial role in the crossover from three to two dimensions in magnetic films. In t he spatially inhomogeneous case with free boundary conditions the D = infinity model is non-equivalent to the standard spherical one and alw ays leads to the diminishing of T-c(N) relative to the bulk.