Spin-Lattice Coupling of a Kramers Doublet:Co2+in MgO

The spin-lattice coupling constants for the ${\mathrm{Co}}^{2+}$ ion as an impurity in MgO have been measured by using a uniaxial-strain technique. The coupling tensor elements applicable to the change of $g$ factor with strain are $F_{11}=-\frac{69}{\left(\mathrm{unit}\mathrm{strain}\right)}$, $F_{12}=\frac{32}{\left(\mathrm{unit}\mathrm{strain}\right)}$, and $F_{44}=\frac{10}{\left(\mathrm{unit}\mathrm{strain}\right)}$. The coupling tensor relevant to the change of hyperfine splitting with strain is related to that for the $g$ factor by a multiplying factor of 1.74×${10}^{-18\mathrm{}}$ ergs. The point-charge model has been used to evaluate the same coupling constants and the theoretical results agree in sign with the experimental results but are larger in magnitude by about a factor of 9. It is also pointed out that for several ions of the iron group the point-charge model gives remarkably good values for the spin-lattice coupling constants, agreeing in both sign and magnitude with experiment.