Electronic Shielding Parameters and Anisotropic Mössbauer Patterns in Dysprosium Ethyl Sulfate

The Mössbauer effect of the 26-keV gamma transition in ${\mathrm{Dy}}^{161}$ was employed to study hyperfine interactions in single crystals of DyES at 4.2°K. The Dy nuclei experience a magnetic hyperfine interaction $g_0{\beta }_N{H}_{\mathrm{eff}}$ of -446±12 Mc/sec, with $H_{\mathrm{eff}}$ parallel to the $c$ axis of the crystal. The hyperfine field and Mössbauer patterns (parallel and perpendicular to the $c$ axis) are readily interpreted in terms of the symmetry of the hyperfine interaction from the ground Kramers doublet. The measurement of the electric quadrupole interaction is of interest because the $4f$ contribution to the electric field gradient (EFG) is often dominant in rare-earth ions; however, for the ground doublet of DyES, this gradient is very small. This fact allowed a simple and direct measurement of the lattice contribution to the EFG. From this result the ratio $\frac{(1-{\gamma }_{\infty })}{(1-{\sigma }_2)}$ was found to be 262, where ${\gamma }_{\infty }$ is the lattice Sternheimer factor and ${\sigma }_2$ represents the shielding of the $4f$ electrons from the crystalline field. The resolution of the paramagnetic hyperfine spectra was interpreted to show that electronic relaxation times were longer than ${10}^{-8\mathrm{}}$ sec.