Study of Y and Lu iron garnets using Bethe-Peierls-Weiss method

We study here the magnetic properties of Y- and Lu- Iron Garnets using the Bethe- Peierls-Weiss method modified to suit complex systems like these Garnets. We consider these Garnets as described by Heisenberg Hamiltonian with two sublattices (a,d) and determine the exchange interaction parameters J ad , J aa and J dd by matching the exerimental susceptibility curves. We find J aa and J dd to be much smaller than those determined by Néel theory, and consistent with those obtained by the study of spin wave spectra; the spin wave dispersion relation constant obtained using these parameters gives good agreement with the experimental values.