Multiferroic properties of La/Er/Mn/Co multi-doped BiFeO3 thin films

Bi_0.9-xLa_xEr_0.1Fe_0.96Co_0.02Mn_0.02O₃ (BLa_xEFMCO) thin films were prepared by sol-gel method. The grain size, grain boundary resistance, oxygen vacancies and the amount of Fe²⁺ of the films were reduced by multi-ion doping to reduce the built-in electric field of the films. An applied voltage was adopted to regulate the effects of the directional alignment of the oxygen vacancies, defects, and defect pairs on the ferroelectric domains at the grain boundaries to control the ferroelectric polarization of the films. Meanwhile, the capacitance peak also reveals the effects of the ferroelectric domains switching, the migration of oxygen vacancies, and the directional alignment of defect pairs on the ferroelectric properties. In addition, the remnant polarization value of the BLa_0.01EFMCO thin film reaches 152?μC/cm², the squareness of the hysteresis loop (R_sq) is calculated to be 1.03, and the maximum switching current is 1.50?mA. The typical butterfly curves under positive and negative electric fields indicate the films with the enhanced ferroelectric properties. Moreover, the BLa_0.01EFMCO thin film exhibits the enhanced ferromagnetic properties, and its saturation magnetization (M_s) is 2.32 emu/cm³. Therefore, the ferroelectric properties of the BFO film can be enhanced by the multi-ion doped BFO film to reduce the grain boundary resistance (Rgb), the interface Schottky barrier formed by the asymmetric electrode material at the top and bottom of the film, and the built-in electric field formed by the film internal defect or defect pairs.