Neutron scattering studies of intermediate-valence compounds

Recent progress in the study of unstable valence compounds by inelastic neutron scattering is discussed. Deeper understanding of the ground state of Sm-based mixed valence compounds results from powder and single-crystal neutron spectroscopy of Sm spin-orbit transitions in a wide energy range. Spin-gap systems with a complicated spectral shape of the magnetic response at low temperature have been found among Ce- and Yb-based compounds, They can be considered as a separate group among unstable valence systems: both crystal field effects and hybridization with conduction electrons appears to be sizable and of comparable magnitude. In heavy fermion compounds the interplay of crystal field interactions and hybridization effects in a relatively large temperature range appears to be an important Factor for the Formation of the magnetic excitation spectra. Pronounced anomalies have been discovered in the lattice dynamics of the intermetallic system Ce-Ni in relation with the intermediate valence state of Cc. (C) 2000 Elsevier Science B.V. All rights reserved.