Variation of f-electron localization in diluted US and UTe

The temperature dependence of the magnetization, the electrical resistivity, and the Hall effect has been measured for 11 different uranium concentrations in single crystals of UxLa1-xS and is compared with corresponding data for U-0.2(La0.15Y0.85)(0.8) and UTe and UTe. While the electrical transport data for diluted UTe show maxima related to crystal-field splittings, such structures are absent in all sulfide compounds. The magnetic susceptibility of the sulfides, measured up to 1200 K, is fitted by the sum of a Curie-Weiss and a Pauli paramagnetism term in second-order approximation. In a quasi-free-electron model the variation with the uranium concentration of the Fermi energy, the carrier concentration and the effective mass is derived. It is found that the degree of localization varies nonmonotonically and, in a certain range, contrary to the U-U separation. It is concluded that hybridization and magnetic exchange play dominant roles.