Structural transition, defect complexes and improved ferroelectric behaviors of Bi0.88Sr0.03Gd0.09Fe0.94Mn0.04Co0.02O3/Co1-xMnxFe2O4 bilayer thin films

Abstract

Bi0.88Sr0.03Gd0.09Fe0.94Mn0.04Co0.02O3/Co1-xMnxFe2O4 (BSGFMC/CMxFO) bilayer thin films were successfully prepared by the sol-gel method. There exists a structural transition from the co-existence of trigonal-R3c:H and trigonal-R3m:R phases to a single trigonal-R3m:R phase in the BSGFMC layer, which is induced by Mn-doping in the CoFe2O4 layer. The amount of oxygen vacancies in the bilayer films is reduced by Mn-doping, leading to a decreased amount of defect complexes. The dielectric dispersion of the BSGFMC/CMxFO bilayer films also disappears with the increase of Mn content. The BSGFMC/CM0.3FO bilayer film exhibits saturated polarization at a lower applied voltage compared with the other samples, while, a large remnant polarization (106 μC cm−2) and a small coercive field (263 kV cm−1) are obtained in this bilayer film. The capacitance-voltage behaviors further confirm its impressive ferroelectric performance. The excellent ferroelectric properties of the BSGFMC/CM0.3FO bilayer film mainly result from the presence of fewer defect complexes and the structural transition in the BSGFMC layer. In addition, the BSGFMC/CM0.3FO bilayer film also displays a giant saturation magnetization with 45.91 emu cm−3. The superior multiferroic properties provide a potentially enable application in novel multiferroic devices.