Induced quadrupole effects near a crossover in a tetragonal TbLiF4 sheelite in a strong magnetic field up to 50 T

The anomalies of magnetic properties of TbLiF 4 caused by the interaction of the energy levels of a rare-earth ion in a strong magnetic field up to 50 T directed along the [100] and [110] axes are studied experimentally and theoretically. The jumps in magnetization M ( H ) and the maxima of the differential magnetic susceptibility dM ( H )/ dH are found in critical fields H c = 28 and 31 T, where the lower component of the excited doublet approaches the ground-state singlet of a Tb 3+ ion. Based on the crystal-field model with known interaction parameters, we calculated the Zeeman effect and the magnetization and magnetic susceptibility curves for the TbLiF 4 crystal, which adequately describe magnetic anomalies and critical parameters of a crossover. It is shown that the jumpwise change in the α- and γ-symmetry quadrupole interactions in TbLiF 4 caused by changes in the corresponding quadrupole moments during the crossing of energy levels leads, in accordance with experiments, to a decrease in the critical field H c by approximately 4 T and an increase in the maximum of the differential susceptibility dM ( H )/ dH near the crossover more than twofold. This behavior can be considered as an analog of the induced quadrupole transition caused by a change of the ground state of the rare-earth ion during crossover.