EPR of Gd3+ in Some Rare Earth Trifluoride Single Crystals

Abstract

The EPR of Gd³⁺ ion has been observed in LaF₃ and the paramagnetic CeF₃, PrF₃, and NdF₃ single crystals at room temperature. The spectra exhibit, on the whole, similar over‐all features in these homologous isostructure rare earth trifluorides, REF₃. The crystal field parameters $b_2^0$ and $b_2^2$ increase progressively with decrease in the difference in ionic radii of Gd³⁺ and the RE³⁺ ion of the host crystal, with variation of $b_2^0$ being linear. On the basis of an explanation which is offered for variation of the parameters $b_n^m$ in a series of similar crystal, an order‐of‐magnitude calculation of the changes in $b_2^0$ is found to be in reasonably good agreement with experiment. The EPR spectra are consistent with $C_{\text{2υ}}$ symmetry of the local crystalline field for Gd³⁺ in all the REF₃, and the orientation of the $y$ axis of the spectra is such that it convincingly supports the $C_{\text{6υ}}^3$ structure for these crystals but not the $D_{\text{3d}}^4$ structure. The Gd³⁺ line‐widths are widely different in these crystals and show an unusual variation in the paramagnetic REF₃. The widths of the transitions $\text{M\hspace{0.17em}↔\hspace{0.17em}M\hspace{0.17em}−\hspace{0.17em}1}$ increase progressively as $M$ takes the values $\frac{1}{2}\mathrm{,\; (}\frac{3}{2}\mathrm{or}\mathrm{-\hspace{0.17em}}\frac{1}{2}\mathrm{),\; (}\frac{5}{2}\mathrm{or}\mathrm{-\hspace{0.17em}}\frac{3}{2}\mathrm{),}\mathrm{and}(\frac{7}{2}\mathrm{or}\mathrm{-\hspace{0.17em}}\frac{5}{2})$ . This variation in the paramagnetic REF₃ is presumably due to the unequal influence of exchange interaction upon various transitions.