Magnetic-field-induced antiferromagnetic-antiferromagnetic phase transition in quasi-two-dimensional multiferroic material Ba₂FeSi₂O₇

We investigate the magnetoelectric property of a quasi-two-dimensional magnet Ba₂FeSi₂O₇. An in-plane magnetic field induces a phase transition that is accompanied by only a small magnetization anomaly but apparent electric polarization change. Our numerical simulation using a mean-field Hamiltonian reveals that the transition is associated with a change in the magnetic wave vector from k = (1 0 1/2) to (1 0 0), which originates from the competition between the intralayer Dzyaloshinskii-Moriya (DM) interaction and the interlayer antiferromagnetic exchange interaction. We determine the sign of the DM interaction from the magnetoelectric behavior in the k = (1 0 0) state. We find that the sign of the DM interaction is opposite to that in the case of Ba₂CoGe₂O₇, which is another well-studied isostructural multiferroic material belonging to the melilite family of compounds. (author)