CRYSTAL-FIELD INDUCED ANISOTROPY IN RARE-EARTH INTERMETALLICS AS STUDIED BY GD-155 MOSSBAUER-SPECTROSCOPY

We have investigated the effect of substitution and nitrogenation on t he hyperfine parameters in Gd2Fe17-x(Ga,Al)(x) (x = 1-10) and Gd(Fe,Co )(12-x)Mo-x(N-y) (x = 1.5-3.0 and y approximate to 1) by means of Gd-1 55 Mossbauer spectroscopy. We have observed marked changes in the valu es of the electric field gradient V-zz, the effective Gd-hyperfine fie ld, and isomer shift. Al substitution in Gd2Fe17 leads to a sign rever sal of the electric field gradient. No sign reversal of V-zz has been observed in the Gd2Fe17-xGax compounds. The effective hyperfine fields of the Gd2Fe17-x(Ga,Al)(x) compounds are decreasing with increasing x , due to the reduction of the 6s electron polarization resulting from the decreasing Fe moments. The ultimate value of the isomer shift base d on a simple model on chemical effects that would be reached for x = 17 is 0.52 mm s(-1) for Al and 0.64 mm s(-1) for Ga substitution in Gd 2Fe17, respectively. The electric field gradient of the GdFe12-xMox co mpounds were obtained for x = 1.5 and x = 3.0. Nitrogenation is shown to lead to a sign reversal of the 4f and Fe sublattice anisotropy. Mo substitution in GdCo12-xMox shows a decreasing negative value of V-zz with increasing Mo concentration x. The values \H-eff\ in GdCo12-xMox increase with increasing Mo concentration. This can be attributed to a different near neighbor Gd and 3d-metal contribution to the effective hyperfine field compared to those of GdFe12-xMox. (C) 1996 American I nstitute of Physics.