Raman study of BiFeO3 with different excitation wavelengths

Raman spectra of bismuth ferrite (BiFeO3) over the frequency range of 100–1500 cm−1 have been systematically investigated with different excitation wavelengths. The intensities of the two-phonon modes are enhanced obviously under the excitation of 532 nm wavelength. This is attributed to the resonant behavior when incident laser energy closes to the intrinsic bandgap of BiFeO3. The Raman spectra of BiFeO3 excited at 532 nm were measured over the temperature range from 77 to 678 K. Besides the abnormal changes of the peak position and the linewidth of the A1 mode at 139 cm−1, the prominent frequency shift, the line broadening and the decrease of the intensity for the two-phonon mode at 1250 cm−1 were observed as the temperature increased to Néel temperature (TN). All these results indicate the existence of strong spin–phonon coupling in BiFeO3.