| Multiferroic materials are those in which two or more of the properties of ferromagnetism(or antiferromagnetism ferrimagnetism), ferroelectricity (antiferroele-ctricity) and ferroelasticity coexist and are coupled. Multiferroic magnetoelectric materials have potential for practical applications in the novel multifunctional devices. Therefore, more and more research have been done about this kind of materials.However, there are very few single-phase materials in nature and the magnetoelectric effects of single-phase materials are usually very weak and only exhibit at low temperatures. At present, it is only known that BiFeO3 has a Curie (or Neil temperature) which is higher than room temperature, but the magnetoelectric effect between ferroelectric-antiferrmagnetic in BiFeO3 is so weak that it can not meet the actual use of the device. Therefore, many new single-phase ME materials and the mechanism of them are still in experimental exploration. At 1972 Van Suchtelen, etc. in the Dutch Philips laboratory proposed to make composite ME materials by mixing piezoelectric phase and magnetic phase. This proposal opened a new preparation method for ME material. Composite materials can achieve great magnetoelectric coupling effect at room temperature, which makes new storage device based on the integrated effect of ferroelectric-magnetic and ME device possible. Now composite ME materials have became a new hotspot for researchers around the world.In this paper, we explored the preparation technology of ferroelectric-ferro-magnetic bilayered films and the multiferroic properties of the bilayered films. The ME effect of this composite film is mainly realized by the strain of the interface, so we need choose ferroelectric material with big piezoelectric constant and ferro-magnetic with big magnetoconstriction coefficient. Currently, composite magneto-electric materials often use Pb (Zr0.52 Ti0.48)O3 (PZT) as ferroelectric materials, mainly due to its high mechanical coupling coefficient, good piezoelectric activity and big mechanical quality factor, etc.. But the main component of PZT is Pb, which is harmful to human body and the environment, and it has been banned by the European Union, so we urgently need lead-free piezoelectric ceramic to replace it. Na0.5K0.5-NbO3 (KNN) belongs to perovskite structure, with a Curie temperature of 415℃, piezoelectric constant d=160 pC/N, and it's trapezius phase at room temperature, which is considered to be one candidate for PZT piezoelectric ceramic materials. CoFe2O4 (CFO) has spinel structure, with big magnetostrictive coefficient, and is widely used in the composite films as magnetic material.This thesis focused on the preparation technology and multiferroic properties of PZT-CFO and KNN-CFO bilayered films. We made bilayered films via RF sputtering method, explored and found the best conditions by trying a variety of preparation conditions such as changing temperature, atmosphere, annealing condition, substrate, and applied extra electric field, etc.. And we discussed the crystal texture, micro-structural, magnetic property, dielectric property, ferroelectric property and the coupling effect between ferroelectric-ferromagnetic. The main content and specific conclusion are as follows:First, we choosed (K0.5Na0.5)NbO3 as ferroelectric target, using magnetron sputtering method prepared (K0.5Na0.5)NbO3 film on different substrates (Pt/Ti/(100) Si, ITO/(100) Si, (100) and (111) Nb doped SrTiO3 substrates) under different temperature. Then we tested the structure and electric properties and discussed which condition is better for the prepartion of (K0.5Na0.5)NbO3 film.Second, we used CoFe204, (K0.5Na0.5)NbO3 as targets using magnetron sputtering method to prepare multiferroic magnetoelectric materials thin films. The total thickness of the films were kept at about 200 nm, but the relative thicknesses, i.e., thickness fractions of the Na0.5K0.5NbO3 layer and CoFe2O4 layer in the 200 nm films were changed. After that, the bilayered films were gone through post anneal treatment, photoetching technology and prepartion of dot electrode. Then we measured the structure, magnetism, dielectric properties and magnetoelectric properties of the bilayered films. The effect of relative thicknesses for bilayered films was disscussed.Third, we choosed Pb(Zr0.52Ti0.48)O3 as ferroelectric target, using magnetron sputtering method to prepare Pb(Zr0.52Ti0.48)O3 film, we changed temperature and substrate to discusse which condition is better for the prepartion of Pb(Zr0.52Ti0.48)O3 film.Then we used CoFe2O4, Pb(Zr0.52Ti0.48)O3 as targets using magnetron sputtering method to prepare multiferroic magnetoelectric materials thin films. The total thickness of the films were kept at about 200 nm and 300nm, but the relative thicknesses, i.e., thickness fractions of the Na0.5K0.5NbO3 layer and CoFe2O4 layer in the films were changed. After that, the bilayered films were gone through post anneal treatment and photoetching technology and prepartion of dot electrode. Then we studied the structure, magnetism, dielectric properties of the bilayered films, etc.. And the effect of relative thicknesses for bilayered films was disscussed.
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