【作者】 王嘉维；

【导师】 赵永刚；

【作者基本信息】 清华大学 ， 物理学， 2013， 博士

【摘要】 近年来，随着新多铁性材料的不断发现和飞速发展，基于多铁性新材料的探索、耦合机制研究和应用型器件设计等工作成为研究中的热点。然而多铁性材料的研究是一个颇具难度的课题，主要表现在，室温下单相多铁材料匮乏，磁电耦合系数很小等问题。因此探寻室温下具有大的磁化强度、极化强度以及磁电耦合效应的多铁性材料一直是研究工作的重点。六角RMnO₃材料在单相多铁性材料中占据着非常重要的地位，其特有的新奇物性，预示着该材料在物性研究和应用上的潜力。本论文以六角YMnO₃作为研究对象，围绕YMnO₃复合结构及单晶材料中的新奇物性展开，结果如下：利用超高真空磁控溅射系统在（110）取向的YMnO₃单晶衬底上生长Co₄₀Fe₄₀B₂₀薄膜，得到多铁复合结构，通过变化外加磁场方向的测量观察到：非晶CoFeB薄膜的磁化率和矫顽场具有各向异性。进一步的实验和分析表明：导致磁性薄膜具有各向异性磁化率的原因是YMnO₃面内铁电极化产生的应力作用。而矫顽场的各向异性可以用“二相”磁化翻转机制解释，这种机制的产生需要磁性薄膜在非单畴的状态下具备并不太强的各向异性作用力，而六角YMnO₃材料的三聚电畴提供了合适的条件。在多铁复合结构中研究铁电对磁化翻转机制的影响是本研究的特色。因为磁性薄膜的各向异性由铁电引发，并且在室温条件下就具备，因而该研究为进一步实现室温下电场对磁性的控制铺平了道路。此外，研究了（001）取向的YMnO₃单晶的导电性。结果表明，铁电性会对界面肖特基势垒产生调制作用。进一步的研究发现：电场对材料的导电性具有调制作用。这一现象可以用电极注入和抽取载流子引发局部载流子浓度变化的机制来解释。这对于阻态存储器应用具有一定的参考价值。更多还原

【Abstract】 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.更多还原