| The magnetoelectric composite films have not only the ferroelectric and ferromagnetic properties, but also the magnetoelectric coupling properties. Therefore, they have a wide application prospect. As lead based magnetoelectric composite films widely used currently are prone to environmental pollution and harm to human health, the applications of magnetoelectric composite films are restricted. In this paper, the ferroelectric films of Bi4-xLaxTi3O12(BLTO) and ferromagnet films of Ni1-xMnxFe2O4(NMFO) were prepared on Pt/Ti/SiO2/Si substrate by means of the sol-gel method. Two kinds of 2-2 type lead-free magnetoelectric composite films with two different depositional sequences of the composite films were also prepared. The influence of preparation process on the phase compositions, microstructures, properties of ferroelectric films, ferromagnetic films and magnetoelectric composite films were investigated.Firstly, Bi4Ti3O12 (BTO) and BLTO films with different doping amount of La were prepared by the sol-gel method. The results show that, when annealed at 700 ℃, the film is composed of BTO main phase and no impurity phase can be found. BTO film have dense and smooth surface. The interface between the film and the substrate is distinct. Compared with the BTO film without La, the residual polarization and the dielectric constant of the La doped BLTO films increase significantly, while the dielectric loss decreased significantly. It indicates that the doping of La can effectively improve the ferroelectric and dielectric properties of the film. When the doping amount of La is 0.6, BLTO film has the best dielectric properties and ferroelectric properties(Pr = 23.56 μc/cm2, Ps= 26.85 μc/cm2).Next, the NMFO films with different doping amount of Mn were prepared by the sol-gel method. The results show that, when annealed at 650 ℃, the film is composed of BTO main phase and no impurity phase can be found. When annealed at 650 ℃, NMFO film has dense and smooth surface. And the interface between the film and the substrate is distinct. Compared with the NFO film without Mn, the saturation magnetization and residual magnetization of the Mn doped NMFO are significantly improved. This shows that the doping of Mn can effectively enhance the ferromagnetic properties of the film. When the doping amount of Mn is 0.3, NMFO film has the best ferromagnetic properties(Mr= 180.2 emu/cm3, Ms= 412 emu/cm3).Finally, the ferroelectric films of Bi3.4La0.6Ti3O12 and the ferromagnetic film of Ni0.7Mn0.3Fe2O4 were successively deposited on Pt/Ti/SiO2/Si substrate by means of the sol-gel method. Two kinds of 2-2 type lead-free composite magnetic films of Bi3.4La0.6Ti3O12-Ni0.7Mn0.3Fe2O4(BN) and Nio.7Mno.3Fe2O4-Bi3.4La0.6Ti3O12 (NB) were prepared by altering the depositional sequences of the composite films. This paper focuses on the influence of the depositial sequences of film on the microstructure and magnetoelectric coupling properties of the composite films. The results show that the depositional sequences of the composite films have no significant impact on the phase compositions, microstructures and morphologies. The ferroelectric properties of NB are better than BN. But the ferromagnet properties of NB are inferior to BN. With the increase of Hbias, the magnetoelectric coupling coefficient of the NB and BN composite films increase firstly, reach the maximum value and then decrease gradually. The magnetoelectric coupling coefficient of the NB composite film is higher than that of the BN composite film under the same Hbias. For the NB composite film, the maximum magnetic coupling coefficient (78.54 mV/cm · Oe) can be achieved when HBias is 5200 Oe. |
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