Mössbauer studies of mixed and substituted garnets

We report here our57Fe Mossbauer studies on the mixed and substituted iron garnets. Magnetisation studies on substituted SmIG system {Sm3−x Cax} [Snx Fe2−x](Fe3)012 (0.2≤x≤1.8) show that the Tc decreases as x increases. We attribute this to the reduced strength of a-d interaction as a result of dilution of a-site. While the Mossbauer spectra seem to reflect this, an interesting feature is the unresolved hyperfine spectrum seen at 80K for x=1.0, even though the transition temperature (Tc) is 285K. For this concentration, varying the rare earth ion from Sm to Er, results in very similar spectra. We speculate spin glass behaviour for x=1.0. In mixed and substituted garnet system {Gd2.5R0.2Ca0.3} [Sn0.3Fe1.7](Fe3)012 (R=Y, Sm, Eu, Ho and Er), we observe well resolved spectra with no change in the hyperfine field with substitution of rare earth. This is consistant with the dominance of a-d interaction in these systems.