27 Al impurity-satellite NMR and non-Fermi-liquid behavior in U 1 − x Th x Pd 2 Al 3

Non-Fermi-liquid (NFL) behavior in the f-sublattice-diluted alloy system ${\mathrm{U}}_{1\ensuremath{-}x}{\mathrm{Th}}_{x}{\mathrm{Pd}}_{2}{\mathrm{Al}}_{3}$ has been studied using ${}^{27}\mathrm{Al}$ nuclear magnetic resonance. Impurity satellites due to specific U near-neighbor configurations to ${}^{27}\mathrm{Al}$ sites are clearly resolved in both random and field-aligned powder samples. The particular configuration associated with each satellite is identified by comparison of calculated and observed satellite intensities. The spatial mean $\overline{K}$ and rms spread $\ensuremath{\delta}K$ of impurity satellite shifts, which are related to the mean $\overline{\ensuremath{\chi}}$ and rms spread $\ensuremath{\delta}\ensuremath{\chi}$ of the inhomogeneous susceptibility, have been measured in field-aligned powders with the crystalline c axis both perpendicular and parallel to the external field. Satellites corresponding to only one uranium near neighbor were chosen for analysis, since in this case $\ensuremath{\delta}\ensuremath{\chi}(T)/\overline{\ensuremath{\chi}(T)}=\ensuremath{\delta}K/\overline{K}$ independent of the (unknown) spatial correlation of the random susceptibility inhomogeneity. The relatively narrow lines observed at low temperatures suggest that disorder-induced inhomogeneity of the f-ion-conduction-electron hybridization is not the cause of NFL behavior in these alloys: at low temperatures the experimental values of $\ensuremath{\delta}\ensuremath{\chi}(T)/\overline{\ensuremath{\chi}(T)}$ are much smaller than required by disorder-driven models. This is in contrast to results in at least some alloys with disordered non-$f$-ion nearest neighbors to f ions (``ligand disorder''), where disorder-driven theories give good accounts of NFL behavior. Our results suggest that f-ion dilution does not produce as much inhomogeneity of the hybridization strength as substitution on ligand sites.