Optical Measurements on Ferromagnetic Tb(OH)3

Abstract

The principal parameters characterizing the low-temperature magnetic and thermal properties of Tb(OH)3 have been inferred from measurements of optical fluorescence and absorption spectra of single crystals. Zeeman effect measurements in fields up to 36 kOe have determined g-values for various single ion levels; in particular g∥=17.7±0.2 for the ground state. This compares well with the value obtained from magnetization measurements and with the value predicted by a crystal field analysis based on a fit of the observed zero field energy levels. The onset of magnetic order near the Curie point (3.7°K) produces shifts and splittings of the observed spectra. At 1.3°K in zero external magnetic field, the ground state is split by 6.4±0.2 cm−1, which together with the observed g-value implies an effective internal field of 7.8±0.2 kOe parallel to the c axis. This value is close to other estimates based on bulk measurements and shows that the interaction is predominantly, but not exclusively due to magnetic dipole coupling. The existence of a small, additional antiferromagnetic interaction is inferred, and this is supported by the zero-field splittings observed in other levels.

Interactions between ions with orbital angular momentum in insulators

“…Examples of this are given by TbES (Baker and Mau 1967) and Tb(OH), (Scott and Wolf 1969) where J, = 6, and Dy3A1,OI2 (Faulhaber and Hufner 1969) and DyPO, (Wright and Moos 1969) where J, = Y. I n axial crystal fields there are further restrictions required by the nature of the ground state, which are independent of the size of J, and are valuable in the discussion of non-Kramers' ions where all mechanisms may contribute in first order to matrix elements within the four ground states of the coupled pair. Only $Fm' with odd I, I' can contribute to K,, in first order, and if J,<S there are off-diagonal elements of (4.35) for pairs sites with axial symmetry contributing to K,, = KVV, but only %Em' with even values of Z,1' can contribute to these elements.…”