Abstract
We report a Raman-scattering investigation of multiferroic bismuth ferrite epitaxial (-axis-oriented) thin films from to . Phonon anomalies have been observed in three temperature regions: in the phase from 930 to ; at , Néel temperature , and at , 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 disappearance of several Raman modes at is compatible with the known structural phase transition and the orthoferrite space group assigned by Arnold et al. [Phys. Rev. Lett. 102, 027602 (2009)]. The spectra also revealed a noncubic phase from and the same noncubic phase extends through the phase between , in agreement with Arnold et al. [Phys. Rev. B (to be published)], and an evidence of a cubic phase around in thin films that is not stable in powder and bulk. Such a cubic phase has been theoretically predicted by and Gonzalez-Vazquez and Iniguez [Phys. Rev. B 79, 064102 (2009)]. Micro-Raman scattering and x-ray diffraction showed no structural decomposition in thin films during the thermal cycling from .
- Received 25 September 2009
DOI:https://doi.org/10.1103/PhysRevB.81.024115
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