Identifying the Magnetoelectric Modes of Multiferroic BiFeO3

Abstract

We have identified three of the four magnetoelectric modes of multiferroic BiFeO3 measured using THz spectroscopy. Excellent agreement with the observed peaks is obtained by including the effects of easy-axis anisotropy along the direction of the electric polarization. By distorting the cycloidal spin state, anisotropy splits the ±1 mode into peaks at 20 and 21.5 cm−1 and activates the lower ±2 mode at 27 cm−1 (T = 200 K). An electromagnon is identified with the upper ±1 mode at 21.5 cm−1. Our results also explain recent Raman and inelastic neutron-scattering measurements.