The Microscopic Model of BiFeO3...

Many years and great effort have been spent constructing the microscopic model for the room-temperature multiferroic BiFeO3. However, earlier models implicitly assumed that the cycloidal wavevector q was confined to one of the three-fold symmetric axis in the hexagonal plane normal to the electric polarization. Because recent measurements indicate that q can be rotated by a magnetic field, it is essential to properly treat the anisotropy that confines q at low fields. We use the anisotropy energy −K3S6 sin6  cos 6 to confine the wavevectors q to the three-fold axis  = 0 and ±2/3 within the hexagonal plane with  = /2.