Non-Fermi-liquid behavior in R 1− xU xRu 2Si 2 (R=Th, Y and La; x⩽0.07)

Abstract

Single-U-ion properties of heavy-electron compound URu 2Si 2 have been investigated by a series of diluting experiments on R 1− x U x Ru 2Si 2 (R=Th, Y, and La; x⩽0.07). A strong uniaxial magnetic anisotropy of local 5f moments is commonly observed throughout the dilutions. From a large enhancement of χ and C/ T as T→0, we suggest a non-Kramers, magnetic doublet Γ 5 (f 2) to be eminently suitable for the crystal-field lowest level, contrary to general views of low-lying singlets for the periodic system. We further demonstrate the absence of the conventional Kondo effect in all these dilutions. A strong suppression of 5f moments at low temperatures accompanies a non-trivial ln T decrease in ρ and a small change in the magnetic entropy. Specific-heat measurements in magnetic fields up to 12 T have revealed no sign of the residual entropy, eliminating the simple application of the two-channel Kondo theory to the present alloys. We also discuss a puzzling phase transition at 17.5 K of URu 2Si 2 in relation to the single-ion physics, providing our latest results of neutron-scattering experiments under high pressure.