We study Kondo-RKKY competition in the intermetallic compound series Ce(Cu 1-x Ni x )Si 2 (x=0, 0.2, 0.4, 0.6, 0.8, 1.0) by performing X-ray diffraction, electrical resistivity, magnetic susceptibility measurements and Ce-L III-edge X-ray absorption spectra. The results reveal that RKKY interaction dominates and leads to spin-glass behavior at the Cu rich end. For the Ni rich end the Kondo effect prevails and drives the system towards an intermediate-valence regime with nearly quenched magnetism. According to the experimental result, we are able to obtain a phase diagram similar to Theumann's theoretical model. This work also observed non-Fermi-liquid behavior from the ρ(T) and χ(T) measurements at x=0.6, indicating this series to lie in the vicinity of a quantum critical point at this content.
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