Kondo and crystal-field effects of U impurities in dilute (LaU)2Zn17

Single-site properties of the U ion in dilute (LaU)2Zn17, a counterpart of a heavy-electron compound U2Zn17, have been deduced from ρ(T), Χ(T) and Cp(T) measured on single crystals. Remarkable features in the dilute limit have been clarified, which include typical impurity Kondo behavior in ρ(T), large and highly anisotropic Χimp(T), and strongly enhanced Cimp(T)/T with a shoulder in Cimp(T) around 3 K and a huge (record-high among U systems) γimp = 1.55 J/K2·mole-U as T → 0 associated with a low characteristic energy-scale of the system. With these features, the system can be characterized as in the Kondo limit. Indeed, gross features of the data are explained, except for the Hext-dependence of Cimp(T), in terms of the conventional Coqblin-Schrieffer model in the presence of the crystal field with the (5f)3 Γ6 doublet ground state. It is also shown that behavior of dense U2Zn17 is not described as a collection of the U impurities in (LaU)2Zn17. (author)