THE CRITICAL-TEMPERATURE AND EXCHANGE INTERACTIONS OF AN S=5 2 HEISENBERG-ANTIFERROMAGNET ON AN FCC LATTICE/

The critical temperature is calculated as a function of the J(nnn)/J(n n) ratio for an S = 5/2 Heisenberg spin lattice with antiferromagnetic ordering of types I and II on a face-centred cubic lattice. J(nn) and J(nnn) represent, respectively, the nearest- and next-nearest-neighbo ur exchange constants. Both possibilities for ordering of type II, J(n n) antiferromagnetic and ferromagnetic, are considered. The critical r egion is studied by applying the Pade approximant method to the corres ponding high-temperature series expansion of the staggered susceptibil ity. The results presented here provide a useful tool for a straightfo rward interpretation and understanding of experimental data. The appro ach is applied to various experimental systems and the values obtained compared with those provided by other approximations.