Temperature dependence of acoustic and low-energy optic phonons in the multiferroic BiFeO3 studied by inelastic neutron scattering

We report inelastic neutron scattering measurements on the acoustic and low-energy phonons in the multiferroic material BiFeO$_3$. The phonon dispersion in the (200) and (111) zones have been mapped out for temperatures between 300K to 750K. The temperature dependence of the dispersion and phonon intensities will be discussed. Possible connections between the the antiferromagnetic phase transition at 640K and anomalies in the phonon modes are observed.