The Preparation And Multiferroic Properties Research Of BiFeO₃-based/Magnetic Composite Thin Films

The defects,structure and interface of BiFeO3(BFO)films are regulated by ion doping to improve their ferroelectricity,but the ferromagnetism of single-phase BFO films cannot meet the application requirements.The ferroelectric composite film constructed by the composite magnetic layer will lead to the deterioration of ferroelectric property.In this paper,the defects,structure and interfacial effects in BFO films were adjusted by means of multi-ion doping.At the same time,the mechanism of ferroelectric deterioration was investigated by constructing multi-ferromagnetic composite films through the magnetic composite layer.In this paper,Bi0.82-xLa0.18BaxFe0.94Mn0.04Co0.02O3(BLBxFMC)thin films,Bi0.79La0.18Sr0.03Fe0.94Mn0.04Co0.02O3(BLxSFMC)thin films,Bi0.96Sr0.04Fe0.98Co0.02 O3/CoFe2O4(BSFCO/CFO)composite film and Bi0.79La0.18Sr0.03Fe0.94Mn0.04Co0.02 O3/CoFe2-xLaxO4(BLSFMC/CFLxO)composite film were prepared by sol-gel method.The effects of ion doping on the defects,structure,interface of BFO films and the properties of BFO films were studied.The effect of magnetic layer on micro structure and multiferroic properties of thin films was studied.The main contents are as follows:(1)The structure,defects and multiferroic properties of BLBxFMC films were studaed.The addition of Ba2+ causes the structural distortion on the film,which affects the vibration of Bi-O bond and Fe-O bond.Appropriate Ba2+ions reduce the volatilization of Bi3+,the oxygen vacancy concentration and defects in the film,which improve the insulation characteristics of the film.BLB0.02FMC shows a more real and stable ferroelectric electric polarization.Under the applied voltage of 35 V,the residual polarization intensity is 33.05 ?C/cm2,the saturation polarization intensity is 37.12 ?C/cm2,the force field is 348.89 kV/cm,and the rectangularity is 1.00.(2)The structure,defects and multiferroic properties of BL,SFMC films were studied.the structure of BLx SFMC changed from R3c:H and R3m:R two phase coexistence to single-phase R3m:R,reduces the oxygen vacancy concentration and Fe2+ concentration,the film's transmission mechanism towards ohmic conduction mechanism,reduce the effect of built-in electric field of the interface between Au electrode and BL,SFMC depletion layer during polarization,BL0.18SFMC's residual polarization Pr=188 ?C/cm2,rectangular Rsq=1.21,thin film showed enhanced ferroelectricity and good stability;At the same time,the reduced oxygen vacancy will also affect the ratio of Fe2+/Fe3+to increase the super-exchange of Fe-O-Fe bond.The saturation magnetization of BL0.18SFMC is 3.94 emu/cm3,and the film also shows enhanced ferromagnetism.The ferroelectric and ferromagnetic properties of BL,SFMC films can be enhanced by multi-ion doping.(3)The effects of CFO layer on the microstructure,internal defects,leakage current density and multiferroic properties of BSFCO film were studied.BSFCO/CFO film induce structure distortion,after composite the CFO ferromagnetic layer the oxygen vacancy and Fe2+ of composite film has been reduced,this led to the BSFCO/CFO composite film with a smaller conductive leakage flow affect the ferroelectric polarization process,the saturation magnetization of BSFCO/CFO composite film and the remanent magnetization Mr were 73.6 emu/cm3 and 46.7 emu/cm3,but the asymmetry and pinning effect of interface makes the electric hysteresis loop there is a big gap.(4)Studying the influence of the structure,defects,interface and multiferroic performance of the upper BLSFMC induced by the doping of La3+ in the lower CFO.After the bottom layer is doped with La3+,the content of R3m in the composite film increases,the number of defective complex in the composite film is reduced,the insulation characteristics of BLSFMC/CFLxO composite film are improved,the ferroelectric domain nailed at the BSLFMC/CFL0.03O interface is reduced,and the ferroelectric property of BLSFMC layer is released.The residual polarization of BLSFMC/CFL0.03O is 136.82 C/cm2,the degree of rectangularity Rsq=1.20,and the saturation magnetization Mx=90 emu/cm3.Compared with single-phase BLSFMC films,the BLSFMC/CFL0.03O composite films showed excellent ferroelectric properties and greatly enhanced ferromagnetism.