GIANT MAGNETIC ANISOTROPY IN PARAMANETIC Tb-2 (MoO4)(3)

The magnetization curves of single crystal samples of metastable orthorhombic ferroelectric paramagnetic beta '-phase of Tb-2(MoO4)(3) were measured at 4.2K and 78K by means of the induction method in a pulsed magnetic field up to 300 kOe along [001] axis and perpendicular to it. The pulse duration was 0.01 s. The magnetization was highly anisotropic. At T = 78K and in the field of 300 kOe the magnetization along the [001] axis was two times larger than that along the [010] axis. So large a magnetization anisotropy in a paramagnetic state has not been observed before. Hysteresis was observed on the magnetization curves at 4.2K. The hysteresis along [100] direction was produced by the interchange of [100] and [010] axes under the influence of the magnetic field. The existence of the unidimentional paramagnetism at low temperatures and the onset of the metastable ferromagnetic state at high fields was supposed to explain the hysteresis on the magnetization curve along [001] axis at 4.2K. Photoluminescence spectra were measured near helium temperatures. They are in qualitative agreement with the interpretation of the uniaxial magnetic anisotropy by means of the singlet magnetism theory.