Paramagnetic Resonance ofCr3+in Yttrium Oxide

The paramagnetic resonance spectrum of ${\mathrm{Cr}}^{3+}$ in single-crystal yttrium oxide has been observed at microwave frequencies from 9 to 71 kMc/sec at temperatures from 4.2° to 300°K. The spectrum is described in terms of the spin Hamiltonian $\mathcal{H}=g\beta \mathrm{H}·\mathrm{S}+D[{S_z}^2-\frac{S(S+1\mathrm{})\mathrm{}}{3}]$, where $g=1.97\mathrm{}\pm 0.01$, $S=\frac{3}{2}$, and $2D=72.9\pm 0.2$ kMc/sec at 300°K, and 72.7±0.2 kMc/sec at 77°K and 4.2°K.