Preparation And Magnetoelectric Coupling Properties Of BNTZ/BFC,BNTZ/CFO Lead-free Magnetoelectric Composite Films

Magnetoelectronic composite films have wide application prospects in information memory devices,semiconductor devices and magnetoelectronic sensors because of their ferroelectric,ferromagnetic and magnetoelectric coupling properties.Considering the environmental protection factors,the research on replacing lead-based magnetoelectric composite films with lead-free magnetoelectric composite films has become a research hotspot.(1)Bi4Ti3O12(BTO)and Bi3.15Nd0.85Ti3-xZrxO12(BNTZ)powders were prepared by the sol-gel method.The films of BTO and BNTZ with different doping amount of Zr4+(x=0.05,0.1,0.15)were prepared on the Pt/Ti/SiO2/Si substrates by the spin coating method.The results show that the pure phase is obtained when the powders and films of BTO and BNTZ were annealed at 700℃.The films prepared are dense and the interfaces between the films and the substrates are clear and smooth.When doping amount of Zr4+is 0.1,the BNTZ films have the largest value of saturated polarization(Ps=40.81μc/cm2),the smallest value of coercive field(Ec=56.2kV·cm-1)and relatively good dielectric properties.Therefore,in this paper,Bi3.15Nd0.85Ti2.9Zr0.1O12 is chosen as ferroelectric phase in the composite films.(2)Powders and films of BiFeO3(BFO)and Co3+(y=0.05,0.1,0.15)doped BiFe1-yCoyO3(BFC)were prepared by the sol-gel method.The results show that the pure phase is obtained in powders and films of BFO and BFC when annealed at 600℃.The surface of the films becomes denser with the increase of doping amount of Co3+and the interfaces between films and the substrates are clear and smooth.When the doping amount of Co3-is 0.15,BFC films have the best ferromagnetic properties.Therefore,in this paper,BiFe0.85Co0.15O3 is chosen as the ferromagnetic films in the composite films.In addition,CoFe2O4(CFO)ferromagnetic films with different thicknesses were prepared.The surfaces of these films are dense,and the interfaces between the films and the substrates are clear and smooth.The CFO film when spin-coating eleven times has the best ferromagnetic properties(Mr=123.2emu·cm-3,Ms=434.6emu·cm-3).(3)Bi3.15Nd0.85Ti2.9Zr0.1O12/BiFe0.85Co0.15O3(BNTZ/BFC),and Bi3.15Nd0.85Ti2.9Zr0.1 O12/CFO(BNTZ/CFO)magnetoelectric composite flims(the ferroelectric and ferromagnetic films were spin-coated four times)were prepared.The results show that the two composite films have symmetrical hysteresis loops,and the ferroelectric properties of BNTZ/CFO composite films are lower than those of single-phase ferroelectric films.The ferromagnetic properties of BNTZ/CFO composite films(Mr=56.2emu·cm-3,Ms=243.5emu cm-3)are much better than those of BNTZ/BFC composite films(Mr=2.15emu·cm-3,Ms=6.37emu·cm-3).Residual tensile stress exists in ferroelectric films(BNTZ)of the two composite films,but it is larger in BNTZ/CFO composite films.The maximum of magnetoelectric voltage coefficients(αE)of BNTZ/BFC and BNTZ/CFO composite films are 46.6 mV/(cm·Oe)and 231.1 nV/(cm·Oe),respectively.Finally,the effect of thicknesses of CFO on the αE of BNTZ/CFO composite films was studied.The results show that,with the increase of CFO film thickness,αE increases first,reaches the maximum value,then decreases.When the spin coating times of CFO film is seven,the maximum value of αE of BNTZ/CFO composite films is 280.3 mV/(cm·Oe).