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

A prominent band centered at ∼1000-1300 cm-1 and associated with resonant enhancement of two-phonon Raman scattering is reported in multiferroic BiFe O3 thin films and single crystals. A strong anomaly in this band occurs at the antiferromagnetic Neel temperature, TN ∼375 °C. This band is composed of three peaks, assigned to 2 A4, 2 E8, and 2 E9 Raman modes. While all three peaks were found to be sensitive to the antiferromagnetic phase transition, the 2 E8 mode, in particular, nearly disappears at TN on heating, indicating a strong spin-two-phonon coupling in BiFe O3. © 2008 American Institute of Physics.