PHYSICAL REVIEW B VOLUME 27, NUMBER 8 15 APRIL 1983 f-count effects in x-ray-absorption spectra of the 3d levels in Ce and its intermetallic compounds J. C. Fuggle and F. U. Hillebrecht Institut fiir Festkorperforschung der Kernforchunsanlage Julich Postfach 1913, D-5170 Julich, 8'est Germany J. -M. Esteva and R. C. Karnatak Laboratoire pour l'Utilization du Rayonnement Electromagnetique, Batiment 209c, F-91405 Orsay Cedex, France and Equipe (No 719) . de Recherche associee au Centre National de la Recherche Scientifique, Batiment 350, Universite de Paris — Sud, F-91405 Orsay Cedex, France O. Gunnarsson Max Planck I-nstitut -fiir Festkorperforschung, D 7000 Stu-ttgart 80, West Germany K. Schonhammer I. Institut fiir Theoretische Physik der Universitat Hamburg, D 2000 H-amburg 36, West Germany (Received 3 January 1983) The 3d x-ray-absorption spectra of Ce, CeSn3, CeAu, CePd, Ce3Pd5, CePd3, CeNi2, and CeNi5 have been studied. Results of theoretical calculations of the 3d absorption spectra are also reported. Comparison with theory shows that the observed spectra are compatible with photoemission-derived 4f level width-s, arising from hybridization with the conduction states, of 30 — 130 meV and f counts greater than 0. 8, in all the compounds studied. The relative merits of x-ray-absorption spectroscopy as a tool for the study of Ce compounds are briefly discussed. INTRODUCTION The role of the 4f levels in Ce and its compounds is not the same as in most other lanthanides. ' They are clearly not so strongly localized and it is more difficult to treat them theoretically than the very strongly localized levels in, for instance, Gd and its compounds. There is thus a special need for experimental studies of the Ce4f levels. Indeed, in the last few years there has been a veritable boom in valence-band photoemission (see, e. g. , Refs. 5 — 16) care-level x-ray-photoemission (XPS) (Refs. 17 — 25) and x-ray-absorption spectroscopy (XAS) at the 2p edges, ' ' with the aim of deducing the num- ber of Ce4f electrons and the strength of their in- teraction with the other conduction electrons. In this paper we report the measurements and analysis of the 3d absorption spectra of La and Ce com- pounds. These spectra have not been extensively studied before. ' However, they are of interest be- cause the binding energy of the 3d levels permits both XPS and XAS studies, so that it is possible to clarify the influence of multiplet effects on the fine structure. Our purpose here is to show how the shape of the absorption edges can be related to the f counts and the hybridization of the f levels with the other conduction states. For the analysis we use a theory ' which describes both the XPS and the 3d XAS spectra. In an earlier study of the XPS line shape, we estimated the strength of the hybridiza- tion of the f level and these data are used for the present work. Previous XAS investigations of the early lanthanides have shown that the 3d region is dom- inated by transitions of the type, 3d 104f tl 3d94f Il + 1 These transitions occur as strong "white lines" ap- proximately 5 eV below the true threshold (edges) arising from excitation of 3d electrons to the Fermi level (EF ). The edges cannot be easily identified be- cause the 3d~6s and 3d~sd transitions are dipole forbidden and the 3d~6p intensity is very low be- cause the density of 6p states at EF and the matrix elements are both low compared with 3d~4f. The energy of the 3d~4f transition is lower than that 27 4637 1983 The American Physical Society