Composites Of Magnetic And Dielectric Properties Of The Study

Ferroelectric-ferromagnetic composites is a new type of functional materials, which is composed of ferromagnetic and ferroelectric properties, and its magnetoelectric effect(ME) could be realized by product effect of composite of piezoelectric phase and magnetostrictive phase. The magnetoelectric effect(ME) is defined as the dielectric polarization of a material in an applied magnetic field, or an induced magnetization in an external electric field. This effect would make the conversion between electric energy and magnetic energy possible. Generally, there are three aspects of application of the materials: application of ferromagnetic properties or ferroelectric properties, application of ferromagnetic properties and ferroelectric properties, but did not use magnetoelectric effect and application of magnetoelectric effect. It provides opportunities for potential applications as electromagnetic interference, ME memories, waveguides, feedback system, microwave, transducers, actuators and sensors.The main purpose of this paper, we use BaTiO₃/CoFe₂O₄ ferroelectric-ferromagnetic composites as the parent materials, and discuss the ferroelectric properties of this composites. Then the microstructure, surface morphology and dielectrical properties, which the composites coexist with ferroelectric of perovskite structure and ferromagnetic of spinel structure, have been investigated.First, the paper presented a review of the history, progress, and preparation method of ferroelectric, ferromagnetic and ferroelectric-ferromagnetic composites, and gave the definition of ferroelectric-ferromagnetic composites. Then it introduced the conventional solid-state-reaction method, and relevant measurement principles and methods.A series of (1-x)BaTiO₃/x CoFe₂O₄ (x=0,0.15,0.3,0.45 and 1) ceramic have been prepared by conventional solid-state-reaction method. BaTiO₃ and CoFe₂O₄ coexist mutually in the entire sintering process, and the XRD patterns of composites reveals that there is not the chemical reaction to produce the impurity or the intermediate phase formed in both the composites. After the sintering, ceramics should be on the electrode, and then, carried on the polarization and magnetization. The compound ceramics powder XRD analysis indicated the ferroelectricity and the ferromagnetic phase coexists mutually, and each crystal structure did not appear big distortion. The dielectric temperature spectras indicated that the value of dielectric constant is found to be decreased with increase in the content of ferrite in the composite, and obviously, there were two peaks, which were Curie temperature of the ferroelectricity and the ferromagnetic phase. It conformed to the characteristic of magnetoelectricity compound materialsAfter prepared BaTiO₃/CoFe₂O₄ magnetoelectricity ceramics , we also used conventional solid-state-reaction method to prepare (1-x) (Ba_0.8Sr_0.2)TiO₃/x (Co_0.5Cu_0.5)Fe₂O₄ (x=0, 0.15, 0.3, 0.45 and 1) ceramics. The compound ceramics powder XRD analysis indicated the ferroelectricity and the ferromagnetic phases coexisted mutually, and each crystal structure did not appear big distortion. SEM also indicated two phases coexisted. The dielectric temperature spectras indicated that Sr²⁺ and Cu²⁺ reduced the Curie temperature of ferroelectricity (Ba_0.8Sr_0.2)TiO₃ .It was also revealed that Tc, which is closer to ferrite transition temperature rather than ferroelectric transition temperature. The value of dielectric constant was found to be increased with increase in the content of ferrite in the composite, this phenomenon was quite rare in magnetoelectricity compound materials, its may provide the broad application prospect in the electricity storage device.