Synthesis and Crystal Structures of REAgMg (RE=La, Ce, Nd, Eu, Gd, Tb, Ho, Tm, and Yb)

It has been claimed earlier (J. Alloys Comp. 186, 223 (1992)) that Ce2Ni22C2.75 is ferromagnetic at room temperature. In this paper it is shown, with magnetic susceptibility and electrical resistivity measurements, that no ferromagnetic order exists in our Ce2Ni22C2.75 sample down to 1.7 K. Moreover, the temperature dependencies of both magnetic susceptibility and electrical resistivity agree well with the existing theoretical models for intermediate valence fluctuating compounds. This agreement together with X-ray absorption spectroscopy data obtained at two fixed temperatures, 10 and 300 K, clearly give evidence for a nonintegral valence state of Ce in Ce2Ni22C2.75.