Magnetic field control of cycloidal domains and electric polarization in multiferroic BiFeO3...

The magnetic field induced rearrangement of the cycloidal spin structure in the room-temperature
multiferroic BiFeO3 is studied using small-angle neutron scattering (SANS). The cycloid propagation
vectors are observed to rotate when magnetic fields applied perpendicular to the polar axis
exceed a pinning threshold value of ∼5T in the studied crystals. In light of these experimental
results, a phenomenological model is proposed that describes our observations, and we revisit the
microscopic origin of the magnetoelectric effect. A new term describing a coupling between the
magnetic anisotropy and the polarization is proposed to explain the recently discovered magnetic
field induced in-plane electric polarization.