| Multiferroic materials refer to materials with two or more kinds of ferroic orders. And the ferroic orders can usually interact each other with coupling effect. These properties provide it very great value in magnetoelectric memory, magnetic sensors and energy-exchanging devices and attracted a large number of researchers. In recent years, both the single-phase multiferroic and composite multiferroic composed of ferroelectric material and ferromagnetic material with a certain method achieved tremendous development. Wherein, layered composite multiferroic heterostructures have been widely used in the development of multi-function devices because of its high coupling coefficient, flexible components, the new physical properties. In this thesis, we mainly studied the magnetic properties, dynamic magnetic properties and magnetoelectric coupling in classic single-phase multiferroic material BiFeO3 and FeGa/PMN-PT,FeCo/PMN-PT multiferroic heterostructures and FeCo/Ta multilayers in PMN-PT substrate. Details of this thesis are as follows:The enhanced magnetization in Sol-gel prepared BiFeO3 nano-powder is becaused of the destruction of antiferromagnetic structure due to the particle size and sample defects. We found the size resonance by measuring the electromagnetic parameters of different thicknesses BiFeO3 ring samples use the vector network analyzer (E5071c). Weakly ferromagnetic resonance and magnetoelectric coupling effects were found in BiFeO3 ring sample when measure its electromagnetic parameters in magnetic field, the magnetoelectric coupling is caused by DM and stress coupling. Nd atoms was doped in BiFeO3 nano-powder, and it influenced the electromagnetic parameters, weakly ferromagnetic resonance and magnetoelectric coupling effects.Through different preparation conditions, we prepared FeGa/PMN-PT(011) multiferroic heterostructures on PMN-PT (011) by RF magnetron sputtering, researched the effects of different preparation conditions on magnetic of the samples. And in DC sputtering conditions we prepared samples which have favorable magnetoelectric coupling effects. In the preparation of FeCo/PMN-PT multiferroic heterostructures, we could tune the magnetic anisotropy and the natural resonant frequency 1.6GHz-3.1GHz induced by electric field. Magnetoelectric coupling in these structures are implemented by strain coupling piezoelectric phase and ferromagnetic phases, and the drift of natural resonant frequency is caused by the regulation of electric field on magnetic anisotropy of samples.We prepared FeCo/Ta multilayer on PMN-PT (011) substrate by using magnetron sputtering and this structure had never been reported yet. Through changing the thickness of the nonmagnetic layer continuously,. we discovered oscillatory change of parameters of magnetic samples varied with the thickness of the non-magnetic layer. This variety was due to the RKKY exchange coupling between the magnetic layer, and this interlayer exchange coupling could impact on the spontaneous magnetization direction of the magnetic multilayers and the magnetoelectric coupling of the whole structure. By changing the thickness of FeCo layer, we discovered that the effects of the thickness of FeCo layer on magnetic and magnetoelectric coupling of structures. And we achieved the tuning of electric field on magnetic anisotropy 250Oe-480Oe and natural resonant frequency 3.5GHz-5.5GHz in the structure of FeCo (4.5nm)/Ta (5nm) multilayer system, this is a great improvement. This structure may have a high potential application in developing multifunction tunable microwave devices and provide a new direction for improve the property of multiferroic heterostructures. |
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