Spin glass transition and hyperfine parameters in FeO-Al2O3-SiO2glasses

Abstract

AC susceptibility and ⁵⁷Fe Mossbauer spectroscopy measurements are reported for Fe²⁺ aluminosilicate glasses. The frequency dependence of T_f (over a range from 10 to 10⁸ Hz) is described by a Fulcher law. This indicates a progressive spin freezing at T_f, comparable with results reported in Co and Mn aluminosilicate glasses. At T<f the Fe²⁺ glasses order speromagnetically, without angular correlation between Fe²⁺ moments and local-field-gradient axes. A linear correlation between isomer shift and quadrupole splitting distributions is established. This is tentatively attributed to a changing covalency of bonding of six-coordinated Fe²⁺ ions. The wide distribution of quadrupole splitting cannot be interpreted unequivocally but indicates a large distribution of crystal-field parameters.