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 C_p(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 χ_imp(T), and strongly enhanced C_imp(T)/T with a shoulder in C_imp(T) around 3K and a huge (record-high among U systems) γ_imp = 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 H_ext-dependence of C_imp(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.