The Effective Local Field and the Spontaneous Sublattice Magnetization of Ferrous Fluoride,

Using the cluster-variation method in the two-spin cluster approximation we calculated the FeF2 spontaneous sublattice magnetization as a function of temperature. This was accomplished by self consistent calculation of the spontaneous local fields from the evaluation of the magnetization from these physical quantities. The normalized magnetization thus obtained is shown to be significantly different from the Weiss molecular field predictions in the neighborhood of the Neel temperature. The results obtained here are shown to be in much better agreement with experimental values for the spontaneous sublattice magnetization. (Author)