X-ray absorption spectroscopy study of the chemical ordering inUCu5−xMx (M = Ni,Ag) compounds

Abstract

This work reports the x-ray absorption spectroscopy study of the chemical ordering inUCu5−xMx (M = Ni,Ag) compounds. The comparison between the experimental Cu K-edge XANESspectra and theoretical computations based on multiple-scattering theoryshows that standard single-channel calculations are capable of reproducing theexperimental spectra. On this subject, an extensive discussion is presentedconcerning the role of both the cluster size and the final state potential inobtaining a good reproduction of the experimental XANES spectra of theseUCu5-based alloys. The agreement between the theoretical and experimentalspectra points to the existence of crystallographic disorder in bothUCu4Ag and UCu4Ni systems. Possessing the distinct low temperature electrical, magnetic and thermal properties exhibitedby 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 betweenthe RKKY and Kondo interactions as the source of the NFL behaviour observed inUCu4Ni, thus supporting an interpretation of the NFL behaviour in terms of the Griffiths phasemodel.