Dy161hyperfine parameters forC2andC3isite symmetries inDy2O3

Low-temperature Mössbauer spectra of ${}_{}{}^{161}{}_{}{}^{}\mathrm{Dy}$ in ${\mathrm{Dy}}_2$ ${\mathrm{O}}_3$ reveal for the first time a resolved magnetic hyperfine structure (hfs) associated with ${\mathrm{Dy}}^{3+}$ at sites with $C_{3i}\left(S_6\right)$ point symmetry. The magnetic hfs parameter is near that expected for a pure $|J_{\xi }=\pm \frac{15}{2}〉$ Kramers doublet and is about 10% higher than for ${\mathrm{Dy}}^{3+}$ ions at sites with $C_2$ point symmetry in ${\mathrm{Dy}}_2$ ${\mathrm{O}}_3$. A crystal-field parameter $B_2^0$ is deduced from the lattice part of the $C_{3i}$ quadrupole splitting. Both the sign of this parameter and the almost pure $|J_{\xi }=\pm \frac{15}{2}〉$ character of the ground state are shown to be inconsistent with earlier Mössbauer results and crystal-field calculations.