The critical temperature and exchange interactions of an<i>S</i>= 5/2 Heisenberg antiferromagnet on an f.c.c. lattice

Abstract

The critical temperature is calculated as a function of the Jaaa/Jaa ratio for an S=5/2 Heisenberg spin lattice with antiferromagnetic ordering of types I and II on a face-centred cubic lattice. Jaa and Jaaa represent, respectively, the nearest- and next-nearest-neighbour exchange constants. Both possibilities for ordering of type II, Jaa antiferromagnetic and ferromagnetic, are considered. The critical region is studied by applying the Padé approximant method to the corresponding high-temperature serís expansíon of the staggered susceptibility. The results presented here provide a useful tool for a straightforward interpretation and understanding of experimental data. The approach is applied to various experimental systems and the values obtained compared with those provided by other approximations.