Two-phonon coupling to the antiferromagnetic phase transition in multiferroic BiFeO3

A prominent band centered at similar to 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, T-N similar to 375 degrees C. This band is composed of three peaks, assigned to 2A(4), 2E(8), and 2E(9) Raman modes. While all three peaks were found to be sensitive to the antiferromagnetic phase transition, the 2E(8) mode, in particular, nearly disappears at T-N on heating, indicating a strong spin-two-phonon coupling in BiFeO3. (c) 2008 American Institute of Physics.