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 Tf (over a range from 10 to 108 Hz) is described by a Fulcher law. This indicates a progressive spin freezing at Tf, comparable with results reported in Co and Mn aluminosilicate glasses. At T<<Tf 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.