Temperature Dependence of the Hyperfine Coupling ofMn2+in the Oxides: Experimental and Theoretical

We have measured the temperature dependence of the hyperfine constant of ${\left({\mathrm{Mn}}^{55}\right)}^{2+}$ in CaO and SrO between 1.4 and 300°K. Our experimental data are in good agreement with the Debye model due to Simanek and Orbach; we give the parameters obtained from the best fit of experiments with theory. Also, by using a semiempirical model to evaluate the amplitude of the lattice vibrations, we have been able to evaluate directly the constants of the orbit-lattice interaction. With both the Debye model and the semiempirical model, we have evaluated the decrease of the hyperfine constant by the zero-point vibrations. We find that the zero-point phonon contribution is larger in CaO than in SrO.