Virtual-Bound-State Formation in Pd-U Alloys

Measurements have been made from below 2^∘{}K to 300^∘{}K of the electrical resistivity and magnetic susceptibility of Pd-U alloys. Low-temperature specific heats have also been measured for Pd-U and Pd-Th alloys. At low actinide compositions, the electronic specific-heat coefficient and the magnetic susceptibility decrease with concentration and are the same as those of Pd-Ag versus electron/atom ratio, provided valences of 1, 4, and 6 are used for silver, thorium, and uranium, respectively. However, at compositions above 7.5 at.% uranium, the electronic specific-heat coefficient and susceptibility rise quickly with composition, and minima are found in the resistivity-temperature curves. The susceptibility indicates no localized-moment behavior. The results are interpreted by the formation at the Fermi level of uranium-$5f$ virtual bound-state levels, whose width decreases with uranium concentration. The specific-heat data give evidence for a term due to interactions between conduction electrons and spin fluctuations. The negative resistivity-temperature derivatives are attributed to localized spin fluctuations.