Ferromagnetic Eu2+-based oxide glasses with reentrant spin glass behavior

In most amorphous insulating magnets, the magnetic structure is dominated by the random distribution of magnetic moments as well as the predominant antiferromagnetic interaction among them, inevitably leading to a transition from high-temperature paramagnetic to low-temperature spin glass phase. In this paper, we report our discovery of ferromagnetic amorphous oxides with reentrant spin glass behavior. Unlike most oxide glasses, there is a strong tendency for the magnetic interaction of Eu2+ ions to be ferromagnetic in oxide glasses, as obviously indicated by the positive values of Weiss temperature. Comprehensive investigations of low-temperature magnetic properties for the present Eu2+-containing glasses have revealed a typical behavior of reentrant ferromagnets. We discuss the possible mechanisms behind the ferromagnetic interactions, as well as the origin of reentrant spin glass nature, based on the specific electronic structure of Eu2+ compounds.