Magnetic properties of disordered oxides with iron and manganese ions

Magnetic properties of disordered oxides involving oxide glasses have been investigated. Spin glass-like transition is observed for Fe2O3–TeO2 and MnO–TeO2 glasses in temperature dependence of dc susceptibility, although magnetic transition does not take place for MnO–TeO2 glasses with low concentration of manganese ion above 2 K at least. The mechanism of magnetic transition observed for Fe2O3–TeO2 glasses is discussed on the basis of dc susceptibility obtained under conditions of field cooling and zero field cooling, magnetic field dependence of magnetization at low temperatures, and frequency dependence of spin-freezing temperature derived from temperature dependence of ac susceptibility. Magnetic properties of disordered ZnFe2O4 thin film prepared by a radio frequency sputtering method have been also studied. The disordered ZnFe2O4 thin film exhibits ferrimagnetic behavior with high magnetization even at room temperature. At the same time, the thin film shows spin-freezing at around 320 K. Temperature dependence of nonlinear susceptibility leads to a conclusion that this transition is explainable in terms of superparamagnetism with magnetic interaction among clusters.