Preparation And Multiferroic Properties Research Of Bi_1-xEr_xFe_1-y-zMn_yCo_zO₃-Co_1-?Mn_?Fe₂O₄ Thin Films

BiFe O₃?BFO?,as a typical multiferroic material at room temperature,has obtained naturally the centre of research activities.BFO has a high Curie temperature?TC=1103 K?and Neil temperature?TN=645 K?.However,the weak ferromagnetism arising from antiferromagnetic nature and low electrical resistivity seriously hinders the potentially feasible applications.Generally,doping and compositing magnetic material layer can improve the properties of BFO to a certain extent.The enhancement of ferromagnetic property induced by doping is weak,and the magnetic material layer can destroy the ferroelectric property of BFO,which both hinder the enhancement of multiferroic properties and maintain the non-ideal performances.So,in this work,the doping and compositing magnetic material layer both be chosen to alter the multiferroic properties of BFO thin film.The effect on structure and performance due to doping and compositing both be researched.In this work,Bi_1-xErxFe O₃?BExFO?,Bi_0.9Er_0.1Fe_1-zCo_zO₃?BEFCzO?,Bi_1-xErxFe_0.96Mn0.02Co0.02O₃,Bi_0.9Er_0.1Fe_0.98Co0.02O₃-Co1-?Mn?Fe2O4 and Bi_0.9Er_0.1Fe_0.96Co0.02Mn0.02O₃-Co1-?Mn?Fe2O4 thin films have been successfully prepared on fluorine doped tin oxide?FTO?substrates by the chemical solution deposition method.Meanwhile,the effects of co-doping and Co1-?Mn?Fe2O4 layer on structure,dielectric,leakage current density,ion valence,ferroelectric and ferromagnetic properties of BFO thin films were investigated systematically.The results are as follows:?1?The results indicate that there is a structural transition from the typical rhombohedral-R3c:H?BiFe O₃?to two-phase coexistence of rhombohedral-R3c:H and rhombohedral-R3m:R?BExFO?.The abundant Fe2+ ions are observed in BExFO,which induces the larger leakage current.The leakage current density increases with the enhancement of Er3+ ions.The BE0.09 FO thin film show great multiferroic properties.the ferroelectric switching current is 1.42×10-2 A and saturation magnetization is 2.60 emu/cm3.?2?With the incorporation of Co2+ ions,a structural transition from the typical rhombohedral-R3c:H and R3m:R(BE_0.10FO)to two-phase coexistence of rhombohedral-R3c:H and triclinic-P1 is observed.The rhombohedral?35%?/triclinic?65%?morphotropic phase boundary?MPB?is obtained in BEFeC0.02 Othin film.Compared with the BEFO thin film,the oxygen vacancy concentration of BEFCzO thin films reduces,and the leakage current densities also reduce nearly 3 orders of magnitude.The ferroelectric and ferromagnetic properties of BEFCzO thin films also get further improvement.The superior multiferroic properties?Ms¹7.08 emu/cm3,Mr⁶.35 emu/cm3 and Pr⁸0.77 ?C/cm2?are obtained in BEFC0.02 O thin film.?3?A structural transition from typical rhombohedral-R3c:H?BFO?to two-phase coexistence of triclinic-P1 and orthorhombic-Pbmn(BE_0.12FMCO)is observed.The content of Fe2+ ions reduces in BExFMCO thin films.And the ratio of Fe2+/Fe3+ approaches 1:1,which indicates a intensive super exchange between Fe2+ and Fe3+ and great ferromagnetic property.The Er,Mn and Co multi-doping have a weak effect on oxygen vacancy concentration in BExFMCO thin films.BE_0.1FMCO thin film shows great multiferroic properties with Pr⁷9.72 ?C/cm2,Ms⁹.78 emu/cm3 and Mr².1 emu/cm3??4?Bi_0.9Er_0.1Fe_0.98Co0.02O₃/Co1-?Mn?Fe2O4?BEFCO/CM?FO?and Bi_0.9Er_0.1Fe_0.96Mn0.02Co0.02O₃/Co1-?Mn?Fe2O4?BEFMCO/CM?FO?thin films show outstanding ferroelectric and ferromagnetic properties.The ferroelectric and ferromagnetic properties of BEFMCO/CM0.3FO thin film are Pr¹57.8?C/cm2,Ec⁴97 kV/cm,Ms⁵1.47 emu/cm3,Mr²3.53 emu/cm3 and Hc? 692 Oe.The BEFMCO/CM0.3FO composite thin film also shows well electrically writable,ferroelectric switching properties.The ferroelectric and ferromagnetic properties of BEFCO/CM0.3FO thin film are Ms⁷4.9 emu/cm3,Mr³4.1 emu/cm3,Hc⁷20 Oe,Pr¹56.3?C/cm2 and Ec⁴10 kV/cm.The change of ferroelectric property in BEFMCO/CM?FO and BEFCO/CM?FO thin films are origin from the structural transformation of triclinic-P1 phase in BEFMCO or BEFCO layer induced by the transformation from cubic-Fd-3m:2 to trigonal-R-3m:H in CM?FO layer due to the incorporation of Mn2+.The two-phase coexistence is beneficial to the enhancement of ferroelectric property.The change of ferromagnetic property in composite thin films is mainly origin from the CM?FO layer.