Local Non-Fermi-Liquid Anomaly and Inter-Site Effects of 5f Electron Systems

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Single-U-ion properties of heavy-electron compound URuィイD22ィエD2SiィイD22ィエD2 have been investigated by a series of diluting experiments on RィイD21-xィエD2UィイD2xィエD2RuィイD22ィエD2SiィイD22ィエD2(R=Y, Th; x 【less than or equal】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 at T → 0, we suggest a non-Kramers, magnetic doublet ΓィイD25ィエD2 (fィイD12ィエD1) to be eminently suitable for the crystal-field lowest level, contrary to general views of low-lying singlets for the periodic system. We have further confirmed absence of the conventional Kondo effect in all these dilutions. A strong suppression of 5f moments at low temperatures accompanies a non-trivial lnT 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 have also found through neutron-scattering experiments that the periodic system URuィイD22ィエD2SiィイD22ィエD2 undergoes a new phase transition under high pressure.