The Preparation And Application Of Magnetoelectrical Composite Materials

As a multi-functional composite material,the multiferroic material can meet the multi-functional requirements of novelty electronic devices and becomes a research hotspot in the field of materials today.In the multiferroic material system,the magnetoelectric effect generated by the coexistence coupling of the ferromagnetic material and the ferroelectric material has attracted much attention for its coupling mechanism and prospective application prospect.In the field of multiferroics,the exploration of magnetoelectric effect is mostly through the application of an electric field to a ferroelectric material to study the regulation of the magnetic properties of ferromagnetic materials by electric fields.However the purpose of this thesis is to explore the influence of the microstructure and the source of the complex anisotropy on the magnetoelectric coupling in ferromagnetic/ferroelectric heterostructure.Therefore,two kinds of magnetostrictive materials FeSiBC and CoFeB,were prepared in this thesis.Subsequently,the above materials were deposited on a piezoelectric crystalline PMN-PT substrate by oblique sputtering to form FeSiBC/PMN-PT and CoFeB/PMN-PT heterostructures.The magnetoeletric properties of the two heterostructures were studied in detail.The main contents are as follows:1?Preparation of FeSiBC magnetostrictive materials.Firstly,using DC magnetron sputtering technique,different thickness of FeSiBC film was prepared.It is found that when the film thickness exceeds the critical value,an out-of-plane magnetization component will appear,eventually leading to deterioration of soft magnetic properties of the film.By inserting non-magnetic C u layer,magnetic CoFe/CoCu layer into the thick film,the soft magnetic properties,magnetostriction coefficient and piezomagnetic coefficient of the multilayer film(FeSiBC/Y)_n can be controlled.Finally,the best performance parameters of multilayers(FeSiBC/C u)_n were obtained through comparison and these parameters are H_c~1.5 Oe,M_r/M_s=95%,H_k~16 Oe.2?Study on CoFeB soft magnetic materials.In view of the poor performance of FeSiBC film in high frequency,this thesis also studied the preparation conditions of CoFeB film,including oblique sputtering technique.Moreover,during the oblique sputtering,when the tilt angle is small(15°),the magnetic spectrum of CoFe B film appears dual resonance phenomenon by rotation of substrate.However,when the tilt angle is increased to the range of 38°to 55°,the hysteresis loop of the film shows a different bee-like shape.The successful deposition of these two magnetostrictive materials lays a good foundation for the subsequent preparation of ferromagnetic/ferroelectric heterostructure.3?The magnetoelectric properties of FeSiBC/PMN-PT heterostructure.Firstly,the origin of giant uniaxial anisotropy in this heterostructure was explored and it was confirmed that the ferroelectric domains on the surface of PMN-PT could be imprinted into the magnetic thin film to induce anisotropy.Further,the internal causes of loop-like and butterfly-like loops of M_r/M_s-E curves in FeSiBC(oblique sputtering)/PMN-PT and FeSiBC(oblique+H)/PMN-PT heterostructure were further studied,respectively.From the AFM,cross-sectional SEM and fast Fourier transform analysis;it was found that in the obliquely sputtered FeSiBC films,the interface structure formed pining points and energy barriers.This affects the inversion of the surface layer polarization vector of the PMN-PT.In contrast,in FeSiBC(oblique sputtering+induced magnetic field)/PMN-PT heterostructure,the interface between FeSiBC and PMN-PT becomes flat due to the introduction of an external magnetic field,which make it easier to reverse the polarization vector of the PMN-PT surface.So a butterfly-like of Mr/Ms-E curve similar to the stress-electric field curve of the PMN-PT substrate appears.The study of this experimental phenomenon provides a new idea for the reversal of magnetization vectors under electric field.4?The magnetoelectric properties of CoFeB/PMN-PT heterostructure.Firstly,the static magnetic properties of CoFe B/[100]PMN-PT and CoFeB/[011]PMN-PT heterostructures were compared that confirmed the[011]PMN-PT has a greater effect on magnetic thin films because of its abundant domains.Then,the magnetoelectrical properties of CoFeB(150nm,15°inclined sputtering)/PMN-PT heterostructure were further studied.The magnetization vector of this heterostructure can be inverted by 90°under electric field.Meanwhile,the adjustable range of M_r/M_s can be reached 75%.However,for CoFe B(350nm,51°inclined sputtering)/PMN-PT heterostructure,the adjustable range of Mr/Ms-E curve in the[100]direction is only 35%under electric field and in the[01-1]direction,the value of M_r/M_s almost unchanges.It is proved that the magnetoelectric effect can be easily obtained when the film thickness is small and the tilt angle is suitable.