Readdressing of Magnetoelectric Effect in Bulk BiFeO3

After decades of study, BiFeO 3 is still the most promising single-phase multiferroic material due to its large polarization and high operating temperature, drawing much attention. As a typical type-I multiferroic material, the magnetoelectric coupling in BiFeO 3 is deemed to be weak due to the different origins of its ferroelectricity and magnetism. Here, the magnetoelectric effect in bulk BiFeO 3 is readdressed both theoretically and experimentally. Based on the Dzyaloshinsky–Moriya interaction scenario, the magnetoelectric effect in BiFeO 3 is actually strong, with a coupling energy of about 1.25 meV and a magnetism-coupled parasitic polarization comparable to that of the type-II multiferroics. However, such strong magnetoelectric coupling also causes the cycloidal spin structure, which inhibits the observation of linear magnetoelectric coupling in bulk BiFeO 3 . To resolve this contradiction, Sm-substitution is utilized to suppress the magnetoelectric effect and unlocks the weak ferromagnetism. At an optimized composition, such a weak ferromagnetic state can be switched back to the cycloidal state by an electric field, thus realizing electrical control of the magnetism. It has been argued that field-controlled phase transition is a promising path to colossal magnetoelectric effect. It is of pioneering significance for further investigations down this road.