An Effective Field Model of the Amorphous Antiferromagnet

Abstract

An effective field model of an amorphous antiferromagnet is developed assuming a distribution of near neighbour distances and hence a distribution of effective field coefficients between interacting atom pairs. It is shown that such a material is characterized by a symmetrical distribution of the total effective field, which, in the absence of any spin correlation, is approximately Gaussian. The model predicts a precise critical or Néel temperature proportional to the square root of the average number of interacting near neighbours, and an unusual downward curvature of the reciprocal susceptibility variation with decreasing temperature (see Fig. 5 and 6). Two classes of amorphous antiferromagnet are examined: those with and those without magnetically isolated paramagnetic atoms. The limited experimental data support the former class.