Neutron diffraction study of theBiFeO3 spin cycloid at low temperature

Abstract

The reported observation of two anomalies in the intensity of the magnon Raman peaks ofBiFeO3 at 140 and 200 K (Singh et al 2008 J. Phys.: Condens. Mater 20 252203; Cazayous et al 2008 Phys.Rev. Lett. 101 037601) led to the hypothesis that such anomalies might originate from a spinreorientation transition. In order to test this hypothesis, we have used temperature-dependentneutron diffraction to track the evolution of the magnetic configuration in single crystals ofBiFeO3. Our results indicate that there is no average reorientation of the spins. This suggests thatthe magnon anomalies may instead be related to the freezing of modes that do not alter theaverage projection of the spins over the plane of the cycloid, as also reported for multiferroicTbMnO3 (Senff et al 2006 J. Phys.: Condens. Mater 18 2069).