Simplifying strong electronic correlations in uranium: Localized uranium heavy-fermion UM2Zn20 (M = Co, Rh) compounds

The physical properties including magnetic susceptibility, magnetization, specific heat, and dynamic susceptibility chi ''(E) are reported for single crystals of the cubic UM2Zn20 (M = Co, Rh) materials. Maxima in the thermodynamic data at T-max similar to 10 K for both compounds and a broad peak in chi ''(E) at 5 K in UCo2Zn20 of width Gamma=5 meV indicate a heavy-fermion state characterized by a Kondo temperature T-K similar to 20-30 K arising from weak hybridization of f- and conduction-electron states. Anderson impurity model fits to the data in the Kondo limit including crystalline electric-field effects corroborate an ionic-like uranium electronic configuration in UM2Zn20.