Hyperfine Coupling Temperature Dependence:Mn2+in CaO and SrO

The effect of temperature variation on the hyperfine coupling constant of ${\mathrm{Mn}}^{2+}$ incorporated in CaO and SrO has been measured by paramagnetic resonance techniques. The experiments were performed on powders and covered the range from room temperature to slightly above 1000°K. These results supplement those of Walsh, Jeener, and Bloembergen, who found a decided explicit (lattice-vibration) dependence for ${\mathrm{Mn}}^{2+}$ in MgO. If an implicit (thermal-expansion) effect similar to the MgO results is assumed for ${\mathrm{Mn}}^{2+}$ in CaO and SrO, they also exhibit a sizeable explicit dependence. Simanek and Orbach have proposed a mechanism in which excited $s$-like configurations are admixed into the $3d^5$ configuration by the orbit-lattice interaction. Their formula for $A\left(T\right)\mathrm{}$, which assumes a Debye vibration spectrum, is shown to fit the CaO data very well. The SrO results, showing an extreme linearity compared with MgO and CaO, are anomalous in this context. A modification of the phonon spectrum is suggested as a possible explanation.