The dilute Kondo compound, ${\text{Th}}_{1-x}{\text{U}}_x{\text{Ru}}_2{\text{Si}}_2$, displays non-Fermi-liquid behavior but no zero-point entropy; it thus appears to elude description by known single-ion models. It may also provide a clue to the underlying local degrees of freedom in its dense counterpart, ${\text{URu}}_2{\text{Si}}_2$. Here we use high-resolution magnetization studies to cross-check the thermodynamic consistency of previous experiments. Measurement of the field dependence of the temperature scale, $T_F\left(H\right)$, associated with Fermi-liquid behavior probes the nature of the underlying impurity fixed point. We find that $T_F\left(H\right)$ grows linearly with applied field, in contrast to the quadratic form expected for the two-channel Kondo model. We use a scaling argument to show that the observed behavior of $T_F\left(H\right)$ is consistent with the absence of zero-point entropy, suggesting novel impurity behavior in this material. More generally, we suggest the field magnetization as a probe of single-ion physics and make predictions for its behavior in other actinide compounds.

• Received 27 August 2010

DOI:https://doi.org/10.1103/PhysRevB.82.235116