Anomalous phonon excitations associated with strong p–f mixing effect of CeSb and CeBi

Abstract Inelastic neutron scattering experiments revealed a new phonon existing only in the magnetically ordered phases of CeSb and CeBi, where ferromagnetic Ce-ion layers with magnetic moments of 2 μ B appear due to the p–f mixing effect on Γ8 state. The observed new phonon is stretching mode of the Ce–X bond forming the p–f mixing orbital. This fact indicates a novel coupling between electronic states by the p–f mixing and the crystal lattice.