Phonon spectroscopy near phase transition temperatures in multiferroicBiFeO3epitaxial thin films

R. Palai, J. F. Scott, R. S. Katiyar
2010 Physical Review B  
We report a Raman scattering investigation of multiferroic bismuth ferrite BiFeO3 epitaxial (c-axis oriented) thin films from -192 to 1000C. Phonon anomalies have been observed in three temperature regions: in the gamma-phase from 930C to 950C; at 370C, Neel temperature (TN), and at 123C, due to a phase transition of unknown type (magnetic or structural). An attempt has been made to understand the origin of the weak phonon-magnon coupling and the dynamics of the phase sequence. The
more » ... of several Raman modes at 820C (Tc) is compatible with the known structural phase transition and the Pbnm orthoferrite space group assigned by Arnold et al.arnold:09. The spectra also revealed a non-cubic β-phase from 820-930 and the same non-cubic phase extends through the γ-phase between 930-950, in agreement with Arnold et al.arnold2:09, and an evidence of a cubic δ-phase around 1000 in thin films that is not stable in powder and bulk. Such a cubic phase has been theoretically predicted in vasquez:prb09. Micro-Raman scattering and X-ray diffraction showed no structural decomposition in thin films during the thermal cycling from 22-1000.
doi:10.1103/physrevb.81.024115 fatcat:i3tzjcoxvzgh3gsyldcs5n64aa