¹⁵¹Eu nuclear resonant inelastic scattering of Eu ₄As₃ around charge ordering temperature

¹⁵¹Eu nuclear resonant inelastic scattering (NRIS) experiments have been performed on the charge ordering Eu₄As₃ compound from 301 to 406K and the Eu partial phonon densities of states were extracted from the observed spectra. We derived the thermodynamic parameters from inelastic components in the observed NRIS spectra using the sum rules. The mean recoilless fraction shows the softening in the lattice vibration of the Eu ion around the charge ordering temperature in spite of no anomaly in the temperature dependence of average sound velocity. We present by the temperature dependence of mean force constant that the hybridization between the 4f states and the conduction or valence bands in Eu₄As₃ plays a role around the charge ordering temperature and in the valence fluctuating state.