Effect of magnetic annealing on phonon behaviors of nanocrystalline BiFeO 3

Abstract

Influence of magnetic annealing at 823 K up to 10 T (T) on the phonon behaviors of nanocrystalline BiFeO 3 was investigated by Raman spectroscopy. The frequencies of fundamental Raman modes increase obviously with increasing annealing magnetic field, and the intensity of the 1260 cm −1 two-phonon mode decreases. The pronounced anomalies of Raman phonon modes under magnetic annealing are attributed to the change of the spin-phonon coupling due to the modulation of spiral spin order. Furthermore, the temperature dependence of Raman peak positions, for the two prominent modes (147 and 176 cm −1), show no notable anomaly around T N except the sample annealed under 10 T magnetic field; meanwhile, in this sample, another obvious phonon anomaly occurs at ∼150 K (another magnetic phase transition point), which indicate that stronger magnetic annealing with 10 T intensely enhances the spin-phonon coupling, and possibly increases magnetoelectric coupling of nanocrystalline BiFeO 3 due to severely modulation of spiral spin order.