Magnetoelectric Feedback among Magnetic Order, Polarization, and Lattice in Multiferroic BiFeO₃

Abstract

By extensive studies of both neutron and synchrotron X-ray diffraction, we discover that the structure deviates from well-known Debye-Gruneissen predictions below<em> T</em>_N in multiferroic BiFeO₃. At the same time, it exhibits a magnetoelastic effect of ∼0.4%, when it undergoes a spiral magnetic order with an extremely long incommensurate period of 630 Å. We show that this additional electric polarization is proportional to the intensity of magnetic Bragg peaks. When subjected to high magnetic fields, our experiments and Monte-Carlo simulation results indicate that magnetic field of ∼20 T unwinds the spiral magnetic structure and quenches the magnetoelastic effect. This is then accompanied by the reduction of electric polarization of 40 nC/cm². The experimental and theoretical results combined together suggest that antisymmetric Dzyaloshinskii-Moriya interaction play a key role in these phenomena. Our results demonstrate an intriguing positive feedback effect among magnetic order, polarization, and the lattice in BiFeO₃.