Spectroscopic studies of magnetic transitions in TbPO(sub 4).

摘要

Rare-earth orthophosphates, RPO(sub 4) (R = Tb to Lu), crystallize in the tetragonal zircon structure in which R occupies sites of D(sub 2d) symmetry. The R = Tb, Dy, Ho compounds order antiferromagnetically at low temperature with the rare-earth moments parallel to the crystallographic c-axis. In TbPO(sub 4) the magnetic transition is accompanied by a cooperative Jahn-Teller effect involving Tb ion-lattice coupling which induces a tetragonal-to-monoclinic distortion of the crystal lattice and a readjustment of the Tb electronic states as required by the lowering of the rare-earth site symmetry. The laser excitation and emission spectra of TbPO(sub 4) and 0.1% Tb doped YPO(sub 4) single crystals were studied below and above the phase transition temperature. Line shapes of transitions in the stoichiometric compound are unusually broad and asymmetric whereas those for the dilute compound are sharp. The TbPO(sub 4) spectra show an anomalous temperature dependence near the phase transitions, indicating strong interactions of rare-earth ions with environment. Comparison of the optical results with neutron scattering is made.