Elastic and electrical anomalies at low-temperature phase transitions in BiFeO3

Our measured dielectric constant and mechanical response of multiferroic BiFeO3 indicate four phase transitions below room temperature. Features correlate with those reported at 50 K (from a peak in the zero-field-cooled magnetic susceptibility) and 230 K (from splitting between field-cooled and zero-field-cooled magnetic data; Singh et al 2008 Phys. Rev. B 77 144403), and those at 140 and 200 K (from the magnon light scattering cross section; Singh et al 2008 J. Phys.: Condens. Matter 20 25203). The primary order parameter is not the polarization in any of the low-T transitions. Instead, the transition near 200 K shows strong elastic coupling, while that at 50 K is fundamentally magnetic, but magnetostrictively coupled to the lattice. The low-T phase transitions display glassy behaviour. A further anomaly at 140 K interpreted as spin reorientation (Singh et al 2008 J. Phys.: Condens. Matter 20 25203; Cazayous et al 2008 Phys. Rev. Lett. 101 37601) shows only weakly in dielectric and mechanical studies, indicating that it is predominantly magnetic with little coupling to any of the other order parameters.