Elastic properties assessment in the multiferroic BiFeO3 by pump and probe method

We have performed elasticity measurements in the bulk multiferroic BiFeO3 (BFO) using acoustical pump and probe spectroscopy. The sound velocities of the (quasi)-longitudinal and two (quasi)-transverse acoustic waves along three independent directions of the (110) surface have been measured. Moreover, one surface wave and one longitudinal wave propagating perpendicular to the surface have been detected. Based on initial input values of the six independent Cij elastic constants determined by our density functional theory calculations and our eleven experimental velocities, the numerical resolution of the acoustic equations allows us to determine all the Cij elastic constants of BFO. The propagation direction dependence of volume and surface waves phase velocities allows the unambiguous assignment of the waves and, hence, the polarization of phonons.