Measurement of Tunneling and Strain Parameters for Octahedrally Coordinated3d9Ions

Accurate electron-spin-lattice relaxation rates by pulse saturation at $X$ band from 1.5 to 10°K of ${\mathrm{Cu}}^{2+}$ as a dilute substitutional impurity in ${\mathrm{La}}_2$ ${\mathrm{Mg}}_3$ ${\left(\mathrm{N}{\mathrm{O}}_3\right)}_{12}$ · 24${\mathrm{H}}_2$O give a nonexponential EPR recovery, which is described by two direct relaxation processes. The corresponding rates are given by ${\tau }^{-1\mathrm{}}=\frac{Acoth\Delta }{2kT}$, where $\Delta$ is concentration dependent and much larger than the microwave energy. Between 10 and 18°K the single-exponential recovery signal is described by the usual Raman process for a Kramers doublet. The results show the presence of a concentration-dependent tetragonal strain (typically ${10}^{-3\mathrm{}}$) superimposed on the instantaneous Jahn-Teller tetragonal distortion. The tunneling splitting, which is independent of concentration, is 2.8 ± 0.2 ${\mathrm{cm}}^{-1\mathrm{}}$. An estimate is made of some pertinent Jahn-Teller parameters. These results may be indicative of a cooperative Jahn-Teller effect.