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.