Electronic Shielding Parameters and Anisotropic Mössbauer Patterns in Dysprosium Ethyl Sulfate

The M\"ossbauer effect of the 26-keV gamma transition in Dy¹⁶¹ was employed to study hyperfine interactions in single crystals of DyES at 4.2^∘{}K. The Dy nuclei experience a magnetic hyperfine interaction g₀βNHeff of -446±{}12 Mc/sec, with Heff parallel to the c axis of the crystal. The hyperfine field and M\"ossbauer 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 (1-γ_∞)(1-σ₂) was found to be 262, where γ_∞ is the lattice Sternheimer factor and σ₂ 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 sec.