Paramagnetic Resonance of Trivalent Holmium Ions in Calcium Tungstate

Abstract

Paramagnetic resonance has been observed in calcium tungstate containing trivalent holmium ions in sites with tetragonal symmetry. The observed spectrum was fitted to the spin Hamiltonian $\mathcal{H}=g_{\parallel }\beta Hcos\theta S_Z+{\Delta }_x{S}_x+{\Delta }_y{S}_y+A{S}_z{\mathrm{I}}_z$ with $A=0.299\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$ and $g_{\parallel }=13.691\mathrm{}$. The distortion parameter $\Delta ={(\Delta _x^{}{}_{}{}^2+\Delta _y^{}{}_{}{}^2)}^{\frac{1}{2}}$ did not possess a unique value and consequently the absorption line shape was asymmetric, the value of $\Delta$ corresponding to the peak intensity being 0.03 ${\mathrm{cm}}^{-1\mathrm{}}$. These results for ${\mathrm{Ho}}^{3+}$ are contrasted with those published for ${\mathrm{Tb}}^{3+}$ in CaW${\mathrm{O}}_4$ and attention is drawn to the differences in line shape in the two cases. It is found that the lowest level in CaW${\mathrm{O}}_4$/${\mathrm{Ho}}^{3+}$ is of the type