Preparation And Properties Of BDT/CCF Lead-free Magnetoelectric Composite Films

For the past few years,on the one hand,our country has an urgent demand for the miniaturization,lightweight and multi-functional compatibility of functional materials and devices.On the other hand,our country has put forward higher requirements for environmental protection.As a composite material with ferroelectric,ferromagnetic and magnetoelectric coupling properties,magnetoelectric composite films can be widely used in new magnetoelectric sensors,resonators,magnetoelectric transducers and spintronic devices.Therefore,the preparation of environment-friendly lead-free magnetoelectric composite films with excellent performance has become an important issue.In this paper,Bi₄Ti₃O₁₂(BIT)powders were prepared by sol-gel method.And the films of Bi₄Ti₃O₁₂(BIT)and Bi_4-xDy_xTi₃O₁₂(BDT)with different concentration of Dy³⁺were prepared by spin-coating technique.The results show that the pure phase of BIT powder and BDT film can be obtained at 700?.The ferroelectric properties of Bi_3.4Dy_0.6Ti₃O₁₂films are the best,with a maximum remanent polarization(Pr=25.6?C/cm²)and a minimum leakage current density(2.7×10^-5 A/cm²).In addition,it is found that the BDT films doped with Dy³⁺have photoluminescence properties.There is an obvious blue-green emission peak at 481 nm,which corresponds to the energy level transition from⁴F_9/2 to ⁶H_15/2.The narrowest band gap is obtained from Bi_3.2Dy_0.8Ti₃O₁₂ films.Due to the best ferroelectric properties,Bi_3.4Dy_0.6Ti₃O₁₂ was selected as the ferroelectric phase in the magnetoelectric composite films experiment.CoFe₂O₄(CFO)powder was also prepared by sol-gel method.Co Fe₂O₄(CFO)films and Co_1-xCu_xFe₂O₄(CCF)films with different concentration of Cu²⁺have been prepared by the spin-coating technique.The results show that pure CFO powder and pure CCF film can be obtained at 650?.The results show that a small amount of concentration of Cu²⁺can enhance the ferromagnetic properties of CFO films.Co_0.9Cu_0.1Fe₂O₄ films have the best ferromagnetic properties,with a maximum remanent magnetization(186.3 emu/cm³)and a minimum coercivity(499.6 Oe).Because Co_0.9Cu_0.1Fe₂O₄ film has the best ferromagnetic properties,Co_0.9Cu_0.1Fe₂O₄ was selected as the ferromagnetic phase of magnetoelectric composite film in the following experiment.Finally,the magnetoelectric composite films of Bi_3.4Dy_0.6Ti₃O₁₂/Co_0.9Cu_0.1Fe₂O₄ were prepared by sol-gel method and spin coating technology in different annealing atmospheres(air,oxygen and nitrogen).The best magnetoelectric coupling performance(?_E=86.4 m V·cm^-1·Oe^-1)was obtained in oxygen.The results of XRD show that the pure ferroelectric and ferromagnetic phases are obtained.SEM also shows that the surface of the film is compact and the interface is clear.Subsequently,the magnetoelectric composite films annealed in air were pre-polarized.After measuring the magnetoelectric coupling properties,it shows that pre-polarized can indeed increase the magnetoelectric coupling coefficient of the films.