Einfluß der Leitungselektronen auf Kristallfeldzustaende von seltenen Erden in Metallen : Eine Untersuchung mit inelastischer Neutronenstreuung

The influence of conduction electrons on the crystal-field (CF) potential acting on rare earth (RE) atoms was studied by inelastic neutron scattering. The magnetic RE-atoms Pr, Nd, Tb, Dy, Ho, Er and Tm were doped into the isostructural, non-magnetic lattices LaAl$_{2}$, YAl$_{2}$ and ScAl$_{2}$ with concentrations between 0.1 at-% and 2 at-%. Because of this low concentration the interaction between magnetic moments was supressed and single ion CF-parameters and coupling constants between RE-moments and conduction electrons were determined. The CF-parameters for these RE-ions show a typical curve with a minimum near Dysprosium, similar in the three lattices but characterized by a shift of the curves. The coupling constants show also a minimum for Dysprosium and Holmium and an increase for the light and heavy RE-atoms. A simple model taking point charges and the influence of the conduction electrons into account can give a qualitative explanation of the observed CF-parameters. The relative distance of the CF-parameter curves can be regarded as consequence of point charge influence, whereas the sign reversal for the 4th-order CF-Parameters are ascribed to 5 d -conduction electron contributions, not contributing to 6th-order parameters. Furthermore the concentration dependence of the magnetic ions on the magnetic exitation spectrum was studied and for Tm in LaAl$_{2}$ the influence of the onset of the superconducting phase on the CF-linewidths. The relaxation behaviour of Ce in CeAg at normal and hydrostatic pressures (2 up to 2.3 GPa) was measured. The observed increase of the quasielastic linewidth with pressure gives a hint to a growing Kondoinstability of theCe$^{3+}$ ions in CeAg