Magneto-electro-elastic effects in some rare earth molybdates and related properties

Abstract

A giant magneto-electric effect was observed in single-crystal samples of metastable orthorhombic ferro-electric ferro-elastic paramagnetic beta ' phases of rare earth molybdates Tb2(MoO4)3 and TbGd(MoO4)3. The electric polarization in these compounds showed large and sharp changes in pulsed magnetic fields of 100 kOe at 78 K. Magnetic fields applied in a certain direction produced irreversible alterations in ferro-electric domain structure of these compounds that were observed visually. This effect was explained qualitatively in terms of large spin-orbit coupling in rare earth triply positive-charged ions and of interaction between the crystal field and the anisotropic charge density cloud of 4f electrons of rare earth triply charged ions of non-zero angular momentum. Related anomalies in the magnetostriction and in magnetization were also observed. The photoluminescence related to Tb3+ ions was observed at temperatures in the range 4.2-300 K. The most intense photoluminescence takes place in the green part of the spectrum. Here two groups of narrow sharp lines were observed, each group consisting of three lines. The photoluminescence exhibited a strong dependence of the polarization upon the ferro-electric domain orientation. Some applications of the effect are proposed.