| Cwiposit multliferroic materials,especially magnetoelectric composites with favorable ferroelectricity and ferromagnetism,have a very broad application prospect in the field of microeletronic devices due to their high magnetoelectric effect at room temperature.Among them,the flexible polymer-based magnetotlectric composite materials have the advantages of both ceramic and polymer materials,such as the high piezoelectric and dielectric values of caremics,the flexibility and high breakdown field of polymer.In this paper,a ferroelectric copolymer poly(vinylidene fluoide-trifluoroetjylene)(P(VDF-TrFE))with high voltage(d31?20 pC/N)is used as the piezoelectric phase of the magnetoelectric composite material,and the cobalt ferrite with high saturation magnetostriction coefficient CoFe2O4(CFO)is the ferromagnetic phase.P(VDF-TrFE)-based magnetoelectric composite films are prepared hy two different connectivity modes:2-2 layered composite and 0-3 core-shell structured particle composite-XRD.SEM,ferroelectic tester,broadband dielectric spectrrometer and VSM were-used to detect the crystalline phase,composition,micrmstucture,ferroelectric properties,dielectric properties,ferromagnetic properties and magnnetoelectric properties of the composite membranes,By such,some statements are proposed and listed as follows.1)The CFO fims are prepared by the sol-gel method combined with the spin-casting process.It was found that the CFO film have an excellent magnetic property using a 9-layer spinning of the original sol together with an annealing temperature of 700?.The CFO films are subsequently compounded with a ferroelectric copolymer P(VD.F-TrFE),After polarizing the obtained CFO/P(VDF-TrFE)double-layer composite film under a high electrical field of 275MV/m.the P(VDF-TrFE)layer shows the character of normal ferroeletricity.In additionw,also find that the magnetization of this electrically poled CFO/P(VDF-TrFE)film is im proved since the electric field may carause a change in the rsmagnetic anisotropy of the film,also indicating that there is strong magnetoelectric coupling in the film.Consequently,the magnetoelectric voltage coefficient(aE31)of CFO/P(VDF-TrFE)composite film is theoretically fitted.It is found that when the interface coupling coefficient k is 0.5,a large magnetoelectric coupling coefficient of 508.5 mV/cm·Oe can be obtained.2)Three kinds of particle composite magnetoelectric films are prepared using 0-3 model,where P(VDF-TrFE)is the matrix and CFO,CFO@BT and CFO@BT@PDA nanoparticles as the fillers,respectively.The composite film filled with inorganic core-shell particles CFO@BT@PDA exhibits the higher dielectric,ferroelectric(FE)and ferromagnetic(FM)properties than the samples filled with un-coated CFO.Especially for CFO@BT@PDA/P(VDF-TrFE)film,the dielectric constant(?r)reaches 85.7 at low frequency(10-1 Hz)and the maximum polarization value(Pm)reaches 49.5 ?C/cm2 under an electric field of 75MV/m.After thermal polarization under an electric field of 5 MV/m at 110? for 30 min,the saturation magnetization(Ms)of the composite film increases from 52.1 emu/g to 61.7 emu/g,indicating that the composite film has strong magnetoelectric coupling effect.Furthermore,the magnetoelectric voltage coefficient of CFO@BT/P(VDF-TrFE)composite film is calculated by non-self-consistent theory(NSC),and a high ?E33 of 129.75 mV/cm·Oe is obtained when the volume fraction(f)of CFO is 0.075.The above results show that both the 2-2 type CFO/P(VDF-TrFE)film and the core-shell type 0-3 CFO@BT@PDA/P(VDF-TrFE)film have high magnetoelectric voltage coefficients.That can provide a potential candidate for the multiferroic composite films as the memory units and magnetoelectric sensor devices.In addition,the core-shell-stucture flexible magnetoelectric film also provides a good reference for studying composite material with high magnetoelectric effect in the future. |
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