  A prominent band centered at around 1000-1300 cm-1 and associated with
resonant enhancement of two-phonon Raman scattering is reported in multiferroic
BiFeO3 thin films and single crystals. A strong anomaly in this band occurs at
the antiferromagnetic Neel temperature. This band is composed of three peaks,
assigned to 2A4, 2E8, and 2E9 Raman modes. While all three peaks were found to
be sensitive to the antiferromagnetic phase transition, the 2E8 mode, in
particular, nearly disappears at TN on heating, indicating a strong spin-two
phonon coupling in BiFeO3.
