Anomalous phonon softening in intermediate-valence CeNi

Abstract

Inelastic neutron scattering measurements of the phonon dispersion in CeNi have been performed in the [1 0 0]/[0 1 0] plane at temperatures between 10 and 295 K. A general softening of the acoustic phonon frequencies with respect to T=295 K is observed at low temperatures for all measured longitudinal and transverse branches. The largest effect occurs at the zone boundary. Anomalies are observed in the temperature dependencies of the energies of several modes, showing either a minimum or a maximum in the range 100 K< T<200 K. This behaviour is indicative of an unusually strong coupling of valence fluctuations and lattice vibrations.