Spectroscopic Properties of TbAsO4

Abstract
Absorption spectra of Tb3+ in TbAsO4, indicate that this material undergoes a Jahn‐Teller induced phase transition from tetragonal to a lower, probably orthorhombic, symmetry at TD = (25.5 ± 2.5) K. Zeeman spectra with the magnetic field in the basal plane taken below TD, show a large anisotropy which is caused not only by the g‐factor but also by large internal fields. The g‐tensor of the isolated two lowest singlets, which are separated less than 0.6 cm−1 at 1.74 K, is uniaxial with g110 = 17.0 ± 1.0 in the [110] direction. Measurements down to 0.77 K show a magnetic phase transition at TN, = (1.48 ± 0.04) K to an antiferromagnetically ordered state which increases the splitting of the two lowest lying singlets up to (2.62 ± 0.06) cm−1 at 0.77 K.