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Earlier models for the room-temperature multiferroic BiFeO3 implicitly assumed that a very strong anisotropy restricts the domain wavevectors q to the three-fold symmetric axis normal to the static polarization P. However, recent measurements demonstrate that the domain wavevectors rotate so that q rotates within the hexagonal plane normal to P away from the field orientation m. We show that the previously neglected three-fold anisotropy K3 restricts the wavevectors to lie along the three-fold axis in zero field. For m along a three-fold axis, the domain with q parallel to m remains metastable below Bc1 = 7 T. Due to the pinning of domains by non-magnetic impurities, the wavevectors of the other two domains start to rotate away from m above 5.6 T, when the component of the torque t = M x B along P exceeds a threshold value tpin. Since t =0 when m is perpendicular to q, the wavevectors of those domains never become completely perpendicular to the magnetic field. Our results explain recent measurements of the critical field as a function of field orientation, small-angle neutron scattering measurements of the wavevectors, as well as spectroscopic measurements with m along a three-fold axis.
Multiferroic BiFeO3 undergoes a transition from a distorted spiral phase to a G-type antiferromagnet above a critical field H_c that depends on the orientation m of the field. We show that H_c(m) has a maximum when oriented along a cubic diagonal par
First-principles calculations, in combination with the four-state energy mapping method, are performed to extract the magnetic interaction parameters of multiferroic BiFeO$_3$. Such parameters include the symmetric exchange (SE) couplings and the Dzy
We report polarized neutron scattering and piezoresponse force microscopy studies of millimeter-sized single crystals of multiferroic BiFeO$_3$. The crystals, grown below the Curie temperature, consist of a single ferroelectric domain. Two unique ele
The spectroscopic modes of multiferroic BiFeO$_3$ provide detailed information about the very small anisotropy and Dzyaloshinskii-Moriya (DM) interactions responsible for the long-wavelength, distorted cycloid below $TN = 640$ K. A microscopic model
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 axi