Covalency and the Paramagnetic Resonance ofMn++in CdSe

The paramagnetic resonance spectrum of divalent manganese has been measured in a single crystal of CdSe ($C_{6v}^{}{}_{}{}^4$) at 77°K. The parameters are $g=2.003\mathrm{}\pm 0.001$, $A=(-62.7\mathrm{}\pm 0.5)\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $D=(15.2\mathrm{}\pm 0.5)\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $\mathfrak{a}=(+14.3\mathrm{}\pm 1.0)\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $F=(-2.0\mathrm{}\pm 1.0)\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$. It is to be noted that in this hexagonal crystal the effect of the cubic field parameter $\mathfrak{a}$ is comparable to that of the axial field parameter $D$. The large value of $\mathfrak{a}$ is attributed to covalency effects. A comparison of the measured $\mathfrak{a}$ value with $\mathfrak{a}$ values found for ${\mathrm{Mn}}^{++}$ in other wurtzite and zincblende crystals shows that there is a correlation between the magnitude of the $\mathfrak{a}$ value and the amount of covalency. A similar correlation between the value of $D$ and the amount of covalency is also found and accounts for the low value of $D$ in CdSe.