X-ray absorption spectroscopy study of the chemical ordering in UCu5-xMx (M = Ni, Ag) compounds

This work reports the x-ray absorption spectroscopy study of the chemical ordering in UCu5-xMx ( M = Ni, Ag) compounds. The comparison between the experimental Cu K-edge XANES spectra and theoretical computations based on multiple-scattering theory shows that standard single-channel calculations are capable of reproducing the experimental spectra. On this subject, an extensive discussion is presented concerning the role of both the cluster size and the final state potential in obtaining a good reproduction of the experimental XANES spectra of these UCu5-based alloys. The agreement between the theoretical and experimental spectra points to the existence of crystallographic disorder in both UCu4Ag and UCu4Ni systems. Possessing the distinct low temperature electrical, magnetic and thermal properties exhibited by UCu4Ni, our results suggest that Ni doping must induce dramatic changes in the electronic structure, as confirmed by the thermopower measurements. These results point to the imbalance between the RKKY and Kondo interactions as the source of the NFL behaviour observed in UCu4Ni, thus supporting an interpretation of the NFL behaviour in terms of the Griffiths phase model.