| Multiferroic material is a kind of material with two or more kinds of ferroelectrics(including ferroelectricity,ferromagnetism and ferroelasticity).Because of its great application prospects in the fields of new magnetoelectric devices,such as spin electronic devices,high-performance information storage and processing,multiferroic materials have been widely concerned.At the same time,the intrinsic mechanism of multiferroic materials involves many physical fields such as charge,orbit,electron spin and lattice,which has become one of the leading research fields in the world.In this paper,BaTiO3 and Sr2CoMoO6 were used to prepare a series of magnetoelectric materials with excellent magnetoelectric and magnetodielectric properties.Generally speaking,ferroelectric materials process electrical insulation,while magnetic materials process electrical conductivity.The content of low resistivity magnetic materials in magnetoelectric composites plays an important role in the performance of composite materials.If the content of magnetic phase is too low,the magnetic properties of the composite will decrease.If the content of magnetic phase is too high,the leakage current of the composite will increase and the insulation will be poor.In order to solve these problems,on the one hand,it is necessary to design a reasonable composition of the magnetoelectric materials,and the magnetic material can be doped to improve the magnetic properties of the composite.On the other hand,the connectivity of the magnetoelectric composites can be adjusted to improve the large leakage current and poor insulation.In this paper,the 0-3 type magnetoelectric ceramic composites with good magnetoelectric and magnetodielectric properties has been prepared by reasonable component design.This material has realized the change of Sr2CoMoO6 from antiferromagnetism to weak ferromagnetism under the external electric field,and shows certain magnetodielectric properties.In order to further improve the magnetic response under the external electric field and dielectric properties of the material,on the basis of the first step to determine the components,Sr2COMoO6 was doped with Fe,and then BaTiO3 was compounded with Sr2Co1-xFexMoO6 after doping modification to further improve the magnetic and dielectric properties of the composite.In order to further study the coupling effect between BaTiO3 and Sr2CoMoO6,and at the same time restrain the leakage current of the material,the sandwich structure of poly(vinylidene fluoride-trifluoroethylene)(P(VDF-TrFE))-BaTiO3/P(VDF-TrFE)-S r2CoMoO6/P(VDF-TrFE)-BaTiO3 three-phase thick film composite was prepared,which showed more excellent magnetoelectric and magnetodielectric properties.In this paper,the multiferroic properties of the composite were characterized by X-ray diffractometer(XRD),scanning electron microscope(SEM),vibration sample magnetometer(VSM),ferroelectric tester and impedance analyzer.The main conclusions are as follows:(1)In(1-x)BaTiO3-xSr2CoMoO6(x=0.02,0.04,0.06,0.08,0.10,0.12)magnetoelectric composite system,we found that all components of the composite were cubic perovskite structure by analyze the XRD data When x=0.12,the composite appears CoMoO4.Through comparison,we found that when x?0.8,the electrical properties of the composite deteriorated,the P-E hysteresis loop became fat,the dielectric loss increased,and the dielectric relaxation phenomenon was observed.Through analysis,we found that the relaxation phenomenon can be attributed to the Maxwell Wagner relaxation model.When x=0.06,the change of Sr2CoMoO6 from antiferromagnetism to weak ferromagnetism was found after 3 kV/cm electric field was applied to the composite.On the one hand,the bond length of Co-O in the composite was changed,on the other hand,the peripheral electronic arrangement of Co atom changed after polarization.All components show negative magneto-dielectric coefficient,which is attributed to the combination of magnetoresistance effect and Maxwell Wagner effect.(2)In 0.96BaTiO3-0.04Sr2Co1-xFexMoO6(x=0.1,0.3,0.5,0.7)ceramics system,all the samples have relatively strong ferromagnetic properties due to the doping of Fe,which is due to the double exchange effect of Fe-O-Mo in the materials.Compared with the undoped 0.96BaTiO3-0.04Sr2CoMoO6 composite ceramics,the dielectric loss of 0.96BaTiO3-0.04Sr2Co1-xFexMoO6 composite ceramics increased and the hysteresis loop widened.However,due to the improvement of magnetoresistance effect of Sr2CoMoO6 by Fe doping,the magnetic and dielectric properties of the composites have been greatly improved based on the inherent mechanism between magnetoresistance effect and Maxwell Wagner effect.(3)In P(VDF-TrFE)-BaTiO3/P(VDF-TrFE)-Sr2CoMoO6/P(VDF-TrFE)-BaTiO3 layered composite system,when no external electric field is applied,the composite shows weak ferromagnetic properties,which indicates that there are both antiferromagnetism and weak ferromagnetism in the composite when no external electric field is applied.The weak ferromagnetism in the material may be attributed to superexchange effect between Co2+and Mo5+.After polarization,the magnetization of the composite increases and decreases alternately,which originates from the reconstruction of the peripheral electron orbit of the Co atom caused by the bound charge at the interface.At the same time,the magnetodielectric of the material is-10.2%,which is due to the combination of the magnetoresistance effect and the Maxwell Wagner effect.The above results show that both the 0-3 type composite ceramic material and the 2-2 type sandwich-structured composite thick film have better magnetoelectric effect and higher magnetoelectric coefficient,which provide potential candidates for the multiferroic material as storage and magnetoelectric sensor. |
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