Spin-Lattice Coefficients for Gd3+ and Eu2+ in CaF2 and for Gd3+ in CaOf

Abstract

We have measured the spinattice coefficients of Eu2+ and Gd3+ in CaF2 and Gds+ in CaO by studying the effect of uniaxial stress on the EPR spectra of these ions. The experimental data show that fourth-order terms in the spin-lattice Hamiltonian give significant contributions. The valúes of the second-order spin-lattice coefficients are given, and the fourth-order contribution is tentatively identified as due to the change of the cubic field splitting with stress. From the valué of the fourth-order coefficient, we conclude that at least half of the temperature dependence of the cubic field parameter is due to the effect of the lattice expansión.