Mössbauer studies of mixed and substituted garnets

Abstract

We report here our⁵⁷Fe Mössbauer studies on the mixed and substituted iron garnets. Magnetisation studies on substituted SmIG system {Sm_3−x Ca_x} [Sn_x Fe_2−x](Fe₃)0₁₂ (0.2≤x≤1.8) show that the T_c 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 Mössbauer 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 (T_c) 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 {Gd_2.5R_0.2Ca_0.3} [Sn_0.3Fe_1.7](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.