INFLUENCE OF UNSTABLE VALENCE OF CERIUM IONS ON THE CRYSTAL-FIELD IN RENI COMPOUNDS

To examine the effect of hybridization of 4f electrons with conduction electrons on the crystal field potential using neutron spectroscopy, we studied the effects of the crystal electric field (CEF) in intermet allic compounds of the type ReNi, in which chemical substitution is fo llowed by a transition of the cerium ions from an intermediate valence state to the Kondo state. Measurements were performed-both on cerium ions in the compounds Ce1-xLaxNi (x = 0.5, 0.8), where they have a who le-number population of the 4f shell, and on the paramagnetic impurity ion Nd in the series of compounds Re1-xNdxNi (Re = Ce, La, Y), in whi ch the cerium ions are found either in an intermediate valence state o r in the Kondo state. From the neutron inelastic magnetic scattering s pectra on Nd ions, we have reconstructed the crystal field parameters in ReNi compounds and calculated the CEF level diagram of Ce ions in t hese compounds as functions of the inter-ion distances Re-Ni. The resu lts of our calculations are in good agreement with the experimentally determined splitting diagram of the ground-state multiplet of the Ce i ons. We have determined that as the degree of hybridization with the c onduction electrons grows the CEF potential varies considerably and th e effective splitting of the 4f shell of the cerium ions increases. Th e estimated energy scale of the splitting of the ground-state multiple t of the Ce3+ ions in the ReNi CEF (Delta(CEF) similar to 15 meV) turn s out to be commensurate with the Kondo temperature (T-K similar to 14 0 K for CeNi. Analysis indicates that the CEF potential has a substant ial effect on the formation of the valence-unstable ground state of th e f shell in this compound. (C) 1998 American Institute of Physics. [S 1063-7761(98)01205-0].