High-pressure155Gd Mössbauer experiments on Gd intermetallic compounds compared with first-principles band-structure calculations

Abstract

High-pressure ${}^{155}$Gd M\ossbauer measurements on Gd metal, GdCo${}_{5}$, GdRu${}_{2}$Si${}_{2}$, and Gd${}_{2}$Co${}_{17}$N${}_{3}$ were performed at 4.2 K. The maximum pressures reached were about 18 GPa. The resulting volume reductions of 20--30 % were determined using high-pressure x-ray diffraction. The pressure dependence of the electric-field gradients and hyperfine fields obtained for the first three systems was compared with predictions from first-principles band-structure calculations. Significant changes of the hyperfine parameters are observed, especially for elemental Gd metal. With increasing pressure, an increase of the electron density at the Gd nuclei is found in all compounds. The values of the hyperfine field initially increase with pressure. For Gd metal the induced structural phase transitions result in large changes in the electric-field gradient at the nucleus ${(V}_{\mathrm{zz}})$. The intermetallic compounds show no structural phase transitions and relatively small changes in ${V}_{\mathrm{zz}}.$ The combination of experiment and calculations indicates that the transition-metal magnetic moments decrease at high pressure. Although for zero pressure predictions of the electric-field gradient and the hyperfine fields, based on the calculations, are quite accurate, the calculated pressure dependence of the hyperfine parameters for Gd, GdCo${}_{5}$, and GdRu${}_{2}$Si${}_{2}$ does not in all cases lead to a satisfactory agreement with experiment. The application of pressures therefore may give additional stimulus for the improvement of the theoretical description of band structures and hyperfine parameters.