Study of RE iron garnets using a modified BPW method

We present the results of a study of the magnetic susceptibility of rare-earth iron garnets, R 3Fe 5O 12, with R  Gd, Tb, Dy, Ho, Er and Yb, using a modified Bethe-Peierls-Weiss (BPW) approximation. The modifications enable us to incorporate the six exchange integral constants necessary to describe three-sublattice systems. We have obtained excellent fits to the experimental susceptibilities, from which we determined the exchange constants as parameters. For the case of gadolinium garnets, we have also obtained the spin wave dispersion relation constant D, in excellent agreement with the value obtained from an analysis of the experimental low-temperature specific heat data.