Anomalies in thermal expansion of DyVO4 induced by quadrupolar ordering

The thermal expansion of the DyVO4 crystal has been experimentally and theoretically investigated in the range of the Jahn-Teller structural phase transition. The manifestation of totally symmetric magnetoelastic interactions upon this transition has been studied for the first time. It is found that the temperature dependences of the unit-cell and thermal expansion parameters along the nonactive Jahn-Teller direction in the basal plane for the DyVO4 crystal exhibit characteristic magnetoelastic anomalies at T < T-c due to the ordering of quadrupole moments of Dy3+ ions. The magnetoelastic contributions of the totally symmetric epsilon(alpha 1) and epsilon(alpha 2) and symmetry-lowering epsilon(gamma) modes to the thermal expansion are calculated within the general crystal-field formalism. The total quadrupolar coefficient G(gamma) and magnetoelastic coefficient B-gamma are determined from the spectroscopic and spontaneous deformation data. It is demonstrated that the thermal expansion of the DyVO4 crystal in the tetragonal and orthorhombic phases is well described in the framework of the unified model using a common set of interaction parameters for both phases. (C) 2000 MAIK "Nauka/Interperiodica".