Preparation Of Magnetic Nanoparticle/polyvinylidene Fluoride-trifluoroethylene Copolymer Flexible Composite Film And Its Magnetoelectric Effect

Magnetoelectric materials have become one of the most promising materials because they exhibit both ferroelectricity and ferromagnetism.This unique coupling between ferroelectricity and ferromagnetism can be used in many electronic equipments and devices.With the development of miniaturization and intellectualization of various electronic devices,especially the demand for flexible devices in wearable devices,various flexible magnetoelectric materials have attracted much attention in recent years.Because the magnetoelectric effect of single-phase magnetoelectric materials is often weak,people focus on composite magnetoelectric materials.Among many flexible composite magnetoelectric materials,polymer based composite magnetoelectric materials have become a research hotspot because of their excellent flexibility,good stability and excellent piezoelectric properties.Composite magnetoelectric materials are generally composed of piezoelectric phase and magnetostrictive phase by different ways.Among many polymer piezoelectric materials,P(VDF-Tr FE)is widely used in the piezoelectric phase of composite magnetoelectric materials due to its high piezoelectric coefficient(about 24 PC·N^-1).Ferrite is an important magnetostrictive material.CoFe₂O₄ has a magnetostrictive coefficient of about 200 ppm,and it is an excellent candidate for the preparation of flexible composite magnetoelectric materials because of its many preparation methods.In this paper,the preparation and magnetoelectric properties of P(VDF-Tr FE)/ferrite flexible composites are studied.(1)CoFe₂O₄ nanoparticles were prepared by hydrothermal method.The morphology of magnetic nanoparticles was spherical,and the average diameter was about 250 nm.Spherical morphology and nano size can make the magnetic particles disperse more evenly in P(VDF-Tr FE)matrix.After characterization,CoFe₂O₄ nanoparticles with different weight ratios(5%?30%)and P(VDF-Tr FE)were mixed and dissolved in dimethylformamide solution,stirred evenly,and dried to form 0-3 type P(VDF-Tr FE)/CoFe₂O₄composite magnetoelectric thin films by solution spin coating method.Scanning electron microscopy(SEM)shows that the magnetic particles are uniformly dispersed in the P(VDF-Tr FE)matrix.Fourier transform infrared spectroscopy(FTIR)shows that a small amount of magnetic particles can increase the content of?phase in the film,thus improving the piezoelectric properties.The piezoelectric coefficient d₃₃ test also proves this point.However,the leakage current will surge when the particle content is higher than 20%,which will seriously affect the polarization process of the composite film,thus affecting the final magnetoelectric coupling performance.Finally,the magnetoelectric coupling coefficient of 47.1 m V·cm^-1·Oe^-1,good repeatability and linearity were obtained in the composite film with 20%weight ratio of magnetic particles.(2)Magnetic CoFe₂O₄ particles and CoZn_xFe_2-xO₄ particles were prepared by spontaneous combustion method,respectively,and they were treated by mechanical ball milling.Scanning electron microscopy showed that the size and dispersion of magnetic particles after ball milling were better than those after manual grinding.The magnetostriction measurements show that although a small amount of Zn doping reduces the magnetostriction coefficient of CoFe₂O₄ particles,it greatly improves the piezomagnetic coefficient of the material.Among them,the piezomagnetic coefficient of CoZn_0.1Fe_1.9O₄ increases about 3 times.0-3 type P(VDF-Tr FE)/CoFe₂O₄ composite magnetoelectric films and P(VDF-Tr FE)/CoZn_xFe_2-xO₄ composite magnetoelectric films were also prepared by solution spin coating method.The weight ratio of magnetic particles was 20%.Scanning electron microscopy(SEM)showed that the composite film had a characteristic spherulite structure.Enhanced magnetoelectric coupling coefficient was observed in P(VDF-Tr FE)/CoZn_0.1Fe_1.9O₄composite magnetoelectric films.(3)2-2 type P(VDF-Tr FE)/CoZn_0.1Fe_1.9O₄ composite magnetoelectric thin films were prepared by solution spin coating method.The middle layer is 40?m 0-3 P(VDF-Tr FE)/CoZn_0.1Fe_1.9O₄ composite magnetoelectric film,the weight ratio of magnetic particles is30%?50%,and the upper and lower layers are 20?m pure P(VDF-Tr FE)films.Scanning electron microscopy showed that the layers were well combined,which was superior to the common epoxy resin bonding method.The leakage current of 0-3 type composite magnetoelectric thin film is greatly improved.In the P(VDF-Tr FE)/CoZn_0.1Fe_1.9O₄composite magnetoelectric film with 50%weight ratio of magnetic particles,high magnetoelectric coupling coefficient was observed,and good linearity and repeatability were obtained.