Paramagnetic resonance ofCr3+in tetragonal GeO2

The ESR spectrum of ${\mathrm{Cr}}^{3+}$ in as-grown single crystals of tetragonal Ge${\mathrm{O}}_2$ has been studied at $X$ band at temperatures of 295 and 92 K. For the choice of magnetic axes $\overrightarrow{\mathrm{x}}\parallel \mathrm{}\left[001\right]\mathrm{}$, $\overrightarrow{\mathrm{y}}\parallel \left[1\mathrm{}\overline{1}0\right]$, $\overrightarrow{\mathrm{z}}\parallel \mathrm{}\left[110\right]\mathrm{}$, so chosen to minimize the ratio $\left|\frac{E}{D}\right|$, the spin-Hamiltonian parameters at 92 K are: $g_x=1.979\mathrm{}\pm 0.001$, $g_y=1.983\mathrm{}\pm 0.001$, $g_z=1.977\mathrm{}\pm 0.001$; $\mathrm{}\left|D\right|=0.630\mathrm{}\pm 0.001$ and $\mathrm{}\left|E\right|=0.138\mathrm{}\pm 0.001$ in ${\mathrm{cm}}^{-1\mathrm{}}$; $A_x=16.9\mathrm{}\pm 0.2$, $A_y=16.0\mathrm{}\pm 0.2$, and $A_z=16.0\mathrm{}\pm 0.2$ in units of ${10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$ for ${\mathrm{Cr}}^{53}$ hyperfine interaction; $A_{ax}=2.1\mathrm{}\pm 0.1$, $A_{ay}=1.9\mathrm{}\pm 0.1$, and $A_{az}=1.9\mathrm{}\pm 0.1$ in units of ${10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$, where this tensor represents the superhyperfine interaction with a ${\mathrm{Ge}}^{73}$ nucleus at one of the nearest-cation sites along the $c$ axis. The zero-field splitting, represented by ${\Delta }_0=2\mathrm{}{(D^2+3\mathrm{}{E}^2)}^{\frac{1}{2}}$, is computed to be 1.348±0.003 ${\mathrm{cm}}^{-1\mathrm{}}$. These results are compared with the results of previously reported studies of ${\mathrm{Cr}}^{3+}$ in the rutile-type hosts Ti${\mathrm{O}}_2$ and Sn${\mathrm{O}}_2$. The values of $\mathrm{}\left|D\right|\mathrm{}$, $\mathrm{}\left|E\right|\mathrm{}$, and the zero-field splitting ${\Delta }_0$ are found to decrease in the order Sn${\mathrm{O}}_2$ → Ti${\mathrm{O}}_2$ → Ge${\mathrm{O}}_2$. The core polarization and orbital contributions to the hyperfine field are also compared for these three hosts.