Field dependence of the Spin State and Spectroscopic Modes of Multiferroic BiFeO3...

The spectroscopic modes of BiFeO3 provide detailed information about the very small anisotropy
and Dzyaloshinskii-Moriya (DM) interactions responsible for the long-wavelength, distorted cycloid
that appears below TN = 640 K. A microscopic model that includes two DM interactions and easyaxis
anisotropy is able to closely describe both the zero-field spectroscopic modes as well as their
splitting and evolution in a magnetic field. While only six modes are optically active in zero field,
all of the zone-center modes are activated by a magnetic field. The close agreement with experiment
suggests that the proposed model provides the foundation for future technological applications of
this multiferroic material.