Magnetic And Electric Property Study Based On YMnO₃and YMnO₃Composite Structures

Recently, with the continuous discovery and fast development of the newmultiferroic material, the work of searching, coupling mechanism researching andapplication devices designing et al based on multiferroic material became the hot topicin the researching work. However, there are still a lot of difficulties and challengingtasks for instance single-phase multiferroic materials are rare at room temperature andthe converse magnetoelectric effects are typically too small to be useful. Therefore,searching multiferroic materials with large magnetization internsity, ferroelectric （FE）polarization intensity and magnetoelectric coupling is still the key issue. HexagonalRMnO₃materials play an important role in the single-phase multiferroic materials, sincethe noval property shows the potential of researching and appilcation. In this thesis, wefocused on the hexagonal YMnO₃material. The novel effects were researched based onYMnO₃composite structure and single phase bulk. The main work is as follows:Multiferroic composite structure was fabricated by depositing amorphousferromagnetic （FM） CoFeB films on top of （110） orientaed YMnO₃single crystalsubstrate with magnetron sputtering system. The angular dependent magnetic propertymeasurement demonstrated that large magnetic susceptibility and coercive fieldanisotropy existed in the CoFeB film. Furhter experimental investigation verified thatthe magnetic susceptibility anisotropy originates from the strain effect induced by thein-plane FE polarization of YMnO₃. The coercive field anisotropy is explained by the“two phase” magnetization reversal mechanism, which is appropriate in the FM/YMnO₃composite structure since the non-single domain state and mediate anisotropy forceinduced by trimerization domain structure meets the two phase mechanism requirementwell. The investigation of coupling between magnetic reversal mechanism and FE is anew story in multiferroic composite structure. Since the magnetic anisotropy wascontrolled by FE polatization at room temperature, this work paves the way for thefurther achievement of controlling magnetization by electric-field.In another aspect, the conductivity of the （001） orientated YMnO₃singlecrystal was investigated. The modulation of interfactional Schottky barrier byFE polarization was observed and the conductivity of the sample can be tunedby electric-field. Through systematic experimental investigation, it was demonstrated that this effect may oringinate from the changing of local carriersdensity induced by injection or extraction of the electrode. These results aresignificant for the achievement of resistance storage device.