The critical temperature and exchange interactions of anS= 5/2 Heisenberg antiferromagnet on an f.c.c. lattice

The critical temperature is calculated as a function of the ratio for an S = 5/2 Heisenberg spin lattice with antiferromagnetic ordering of types I and II on a face-centred cubic lattice. and represent, respectively, the nearest- and next-nearest-neighbour exchange constants. Both possibilities for ordering of type II, antiferromagnetic and ferromagnetic, are considered. The critical region is studied by applying the Padé approximant method to the corresponding high-temperature series expansion 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.