Preparation And Properties Of Lead-free Magnetoelectric Composite Thin Films Of Bi_0.5Na_0.5Ti_1-xFe_xO_3-?/NiFe_2-xNd_xO₄

Pb(Zr_1-xTi_x)O₃(PZT)is the most common ferroelectric phase in magnetoelectric composite films.As Pb not only endangers human health but also causes serious pollution to the environment,it is necessary to search for lead-free ferroelectric materials with high ferroelectric performance to replace the PZT-based ferroelectric materials.Lead-free magnetoelectric composite thin films were successfully prepared on Pt(111)/Ti/Si O₂/Si substrates by sol-gel method.And their ferroelectric,ferromagnetic and magnetoelectric coupling properties were investigated.(Bi_0.5Na_0.5)TiO₃(BNT)was selected as ferroelectric phase,and ferroelectric thin films were prepared on Pt(111)/Ti/Si O₂/Si substrate by sol-gel method.Then,BNT films with different layers were prepared.And the effects of layers on the morphology,phase composition and electrical properties of the films were investigated.Subsequently,Fe³⁺doped BNT films with four layers were prepared.The ferromagnetic phase of Ni Fe₂O₄(NFO)was doped with Nd³⁺.Ni F_2-xN_xO₄thin films with different doping content of Nd³⁺were prepared by sol-gel.Finally,Bi_0.5Na_0.5Ti_0.98Fe_0.02O₃films and Ni Fe_1.98Nd_0.02O₄films were selected to prepare the magnetoelectric composite films.The magnetoelectric composite films were prepared on substrates under different deposition order of ferroelectric and ferromagnetic phases.The results show that:the BNT films annealed at 700?have no obvious secondary phase.And they possess smooth surface and compact structure.when the number of layers is 4,the films have the best morphology,the lowest leakage current and the highest remanent polarization.With the increasing doping content of Fe³⁺,the values of leakage current densities of films decrease obviously at first,and then increase slightly.The values of remnant polarization increase at first,and then decrease slightly.When the doping content of Fe³⁺reaches 0.02,the current density decreases to the minimum value(2.026×10^-6A·cm^-2)and the remnant polarization increases to the maximum value(25.2?C·cm^-2).The doping of Nd³⁺does not change the phase composition of the films,When the doping content of Nd³⁺is 0.02,the film of Ni F_2-xN_xO₄possesses a smooth surface and dense microstructure,maximum of saturation magnetization(282.4 emu·cm^-3).Compared with the single film,the remnant polarization and saturation magnetization of the composite films are smaller.The composite films when ferroelectric films were deposited firstly possess the maximum remnant polarization,saturation magnetization and magnetoelectric coupling coefficient.The maximum of magnetoelectric coupling coefficient is169.7m V·cm^-1·Oe^-1.