Temperature dependence ofthe spin-Iattice interaction for Gd3+ in Th02 and ce02

Abstract

The second and fourth order spin-lattice coefficients of Gd3+ in cubic positions of Th02 and Ce02 crystals have been ¡neasured as a function of tempera ture between 4 and 360 °K in electrón pararragnetic resonance experiraents in uniaxially stressed crystals. Important differences in magnitude are obtained for each of the second order coefficients in both lattices ana these coefficients show a large variation v/ith temperature. A detailed theoretical calculation of these coefficients has not been carried out; however it is possible to qualitatively interpret the observed temperature variation in terms of explicit contributions coming from the modulation of the orbit-lattice interactions by the lattice vibrations. The temperature variation curves are explained using an Einstein model for the vibrations of the oxygen ligands of the paramagnetic ions. The fourth order coefficients are similar for bcth crystals and are temperature independent in the studied range. The coefficient related to the effect of a hydrostatic strain on the energy levels of the ion is used to explain the observed temperature variation of the cubic field parameter in terms on iniplicit contributions coming from the thermal expansión of the crystal.