Dynamic Jahn-Teller effect for the chromous ion in KMgF3

The dynamic Jahn-Teller effect for the chromous ion in KMg${\mathrm{F}}_3$ is characterized by acoustic measurements. Acoustic-relaxation measurements and the temperature dependence of the acoustic-paramagnetic-resonance spectra are used in conjunction with theoretical vibronic levels of a molecular-cluster approximation to evaluate the tunnel splitting ($\delta =10\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$) and spin-orbit splitting ($D=1.2\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$). These values ($\delta , D$) are approximately one half those observed for MgO:${\mathrm{Cr}}^{2+}$ where the octahedral coordination of the chromous ion is with oxygen anions compared to fluorine anions in KMg${\mathrm{F}}_3$. The gyromagnetic ratio as well as the internal strains are estimated to be less in KMg${\mathrm{F}}_3$ than in MgO.