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 Ha miltonian with two sublattices (a,d) and determine the exchange intera ction parameters J(ad), J(aa) and J(dd) by matching the exerimental su sceptibility curves. We find J(aa) and J(dd) to be much smaller than t hose determined by Neel theory, and consistent with those obtained by the study of spin wave spectra; the spin wave dispersion relation cons tant obtained using these parameters gives good agreement with the exp erimental values.