Phonon spectroscopy near phase transition temperatures in multiferroicBiFeO3epitaxial thin films
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
... 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.