On the problem of coexistence of the weak ferromagnetism and the spin flexoelectricity in multiferroic bismuth ferrite

On the example of the prototypical multiferroic bismuth ferrite the microscopic origin of the spin flexoelectricity responsible for the spin cycloid ordering is analyzed. It is shown how the three basic structural distortions corresponding to the frozen-phonon modes of an ideal perovskite lattice result in the coexistence of the spin canting and the spin cycloidal ordering. On the basis of a simple formula for the antisymmetric Dzyaloshinskii-Moriya superexchange the inhomogenous magnetoelectric contribution to the theromodynamic potential is derived and the values of the microscopic parameters corresponding to the spin canting and the spin cycloid are determined. Copyright (c) EPLA, 2012