Magnetization and specific heat of amorphous magnets and high-temperature crystalline magnets, S ≥ [formula omitted

Abstract

The magnetization and specific heat of amorphous magnets are calculated for the Ising and Heisenberg models with arbitrary spin S and for mixtures of different spins. We use the Greenfunction technique and carry out the calculations up to the second order retaining only the localized and static correlations. The latter are then calculated self-consistently. The results follow quite closely experimental data. Special results obtained are: a) the polarization of each spin, in the Heisenberg model, is less than S at T = 0 for both ferro- and antiferromagnetic interaction; b) the Curie point, T c, in both models, is suppressed below the mean-field result and may even vanish or not exist under certain conditions; c) there is a critical magnetic-impurity concentration, m c, below which ferromagnetism does not exist; m c is spin dependent and decreases as S increases; d) the specific heat may exhibit two maxima, one at T c and another broad one at a higher temperature. The specific heat in zero magnetic field and at T > T c and the entropy associated with it, are proportional to S ( S + 1).