High-energy Ce-3d photoemission:: Bulk properties of CeM2 (M = Fe,Co,Ni) and Ce7Ni3

We study the photon energy dependence of Ce-3d photoemission in CeM2 compounds (M = Fe, Co, Ni) and in Ce7Ni3 with measurements taken with synchrotron radiation in the photon energy range 1050-3850 eV. The results show a drastic increase of the bulk sensitivity at the higher energies due to the increase of the photoelectron escape depth. The spectra at 3850 eV are largely dominated by the bulk contribution, which is typically 85% of the total intensity in the CeM2 compounds. The results allow us to obtain the bulk contribution to the spectra in CeM, with a procedure presented here and giving the fractional weights of the bulk f(0), f(1), and f(2) configurations. In the CeM2 compounds a correlation is found between these spectral weights and the crystallographic data showing that the hybridization is nonmonotonic versus the atomic number of the transition metal. We discuss the results both in connection with an impurity model and with the available calculations in an itinerant model. Moreover, the results suggest that the bulk hybridization in CeM2 systems with heavy transition metals has been probably underestimated up to now.