Magnetic and crystal-field properties of the magnetic superconductor ${\mathrm{DyNi}}_2$${\mathrm{B}}_2$C from ${}_{}{}^{161}{}_{}{}^{}\mathrm{Dy}$ Mössbauer spectroscopy

We have utilized the ${}_{}{}^{161}{}_{}{}^{}\mathrm{Dy}$ Mössbauer effect to investigate the magnetic properties and the nature of the ground state of the ${\mathrm{DyNi}}_2$${\mathrm{B}}_2$C quaternary magnetic superconductor (${\mathit{T}}_{\mathit{N}}$∼11 K, ${\mathit{T}}_{\mathit{c}}$∼6 K). Detailed analysis of the spectra suggests that the magnetic transition is of first order and the Dy moments of 9.8${\mathrm{\mu }}_{\mathit{B}}$ at saturation are confined in the basal plane. Isomer shift in this material (∼0.5 mm/s) is significantly less than that observed in metallic Dy which implies charge transfer from 6s orbitals of Dy onto the strongly bonded C atoms. The second-order ${\mathit{B}}_2^0$ crystal-field parameter is positive and estimated to amount to about 2 K. The ground-state crystal-field doublet is composed primarily of the |±1/2〉 component of the J=15/2 free ion term. Higher-order crystal-field terms should be included in the exchange crystal-field Hamiltonian for a detailed account of the experimental results. © 1996 The American Physical Society.