Non-Fermi-liquid behavior in R1-xUxRu2Si2 (R = Th, Y and La; x <= 0.07)

Single-U-ion properties of heavy-electron compound URu2Si2 have been invest igated by a series of diluting experiments on R1-xUxRu2Si2 (R = Th, Y, and La: x less than or equal to 0.07). A strong uniaxial magnetic anisotropy of local 5f moments is commonly observed throughout the dilutions. From a lar ge enhancement of chi and C/T as T-->18, we suggest a non-Kramers, magnetic doublet Gamma(5) (f(2)) to be eminently suitable for the crystal-field low est level, contrary to general Views of low-lying singlets for the periodic system. We further demonstrate the absence of the conventional Kondo effec t in all these dilutions. A strong suppression of 5f moments at low tempera tures accompanies a non-trivial In T decrease in rho and a small change in the magnetic entropy. Specific-heat measurements in magnetic fields up to 1 2 T have revealed no sign of the residual entropy, eliminating the simple a pplication of the two-channel Kondo theory to the present alloys. We also d iscuss a puzzling phase transition at 17.5 K of URu2Si2 in relation to the single-ion physics, providing our latest results of neutron-scattering expe riments under high pressure, (C) 2000 Elsevier Science B.V. All rights rese rved.