Magnetism and Magnetic Interaction in a Complex Oxide Glass System Containing Deposited Clusters of Magnetite at the Superparamagnetic State

Abstract

A series of oxide glasses rich in Fe 2+ and Fe 3+ with their various molar ratio has been synthesized, and the magnetic behaviors have been studied by static magnetization and ESR experiments. Near room temperature, superparamagnetic behavior is caused by deposited fine (40–50 A) clusters of iron-oxides. At lower temperatures, though, we observe drastic descending shift of the field for ESR as well as ferromagnetic Curie-Weiss law in the susceptibility. We interpret these behaviors consistently by a classical model, taking into account only an effective interaction between the clusters and the magnetic matrix region. For the glasses of moderate oxidation grades (molar ratio of Fe 2+ to total Fe is in 0.39–0.66), each shifting ESR field also shows a peak anomaly near 100 K caused by Verwey transition of magnetite clusters. Verwey transition is observed evidently for the super fine clusters owing to the protection against oxidation in the glasses.