Study of 4f hybridization in CeNiX with X=Sn_δGe_1-δ, 0≤δ≤1

We report inelastic neutron scattering and core-level X-ray photoemission spectroscopy experiments for studying the Kondo problem in the CeNiX, X=Sn_δGe_1-δ 0≤δ≤1 series. The neutron results confirm that they behave like a Kondo lattice for δ≥0.85, showing broad maxima at around 30 meV, typical of a crystal field magnetic scattering. So, the Ge doping could produce the suppression of the cerium magnetism observed for δ≤0.25. To open a more deep sight on this point, we have analyzed the 3d core-level XPS spectra by using the well-known Gunnarsson-Schönhammer model. From this analysis, we have obtained the "on-site" Coulomb bare repulsion for f states, U, and hybridization parameter, Δ, related with the hopping from the f states to the conduction ones. These U values are very similar for all compounds, about 7 eV, but the hybridization parameter slightly changes from 0.2 to 0.16 eV on increasing the Sn concentration. In Sn-rich compounds, the 4f occupation is close to spin limit fluctuation, which allows us to obtain an estimation of the Kondo temperatures, ≈1200 K, and the static 0 K susceptibility, ≈1.1×10^-3 emu/mol. Finally, we have done "ab-initio" calculations based on the LDA+U+SO which confirm the existence of a small electronic gap opening in the DOS of Ge-rich compounds for U values lower than 7 eV.