有机复合磁电阻器件的制备、界面耦合作用与自旋输运研究

The organic layers used in the present organic hybrid devices are most of an amorphours structure. A large amount of defects in these amorphous layers reduce the carriers mobility and induce spin flip. As a result,the phenomenons of organic hybrid magnetoresistance are mostly observed at low temperature,and the magnetoresistance ratios reported at room temperature are very low. Organic single crystals have some advantages,such as ordered structure、high carrier mobility and highly thermal stability. This project will grow organic layer with special crystal orientations (organic single crystal or polycrystalline with highly ordered texture) on magnetic single crystal substrates, and then develop spin electronic materials and magnetoresistance devices with high magnetoresistance ratio at room temperature. Based on the systemic investigation of the interactions between organic layer and magnetic substrates with different orientations,and new physical phenomenon,such as magnetic hardening, the correlation and mechanism of interface coupling between the magnetic layer and the organic crystal layer will be explored. By the measurement of different devices (GMR, TMR, etc.), the spin dependent transport behaviors in the organic layers with different crystal orientations can be studied and understood. Effective channels and methods for the enhancement of spin injection/tunnelling and the decrease of spin flip in the organic layers will be investigated. This project will provide the fundamental knowledge in both theory and experiment to develop organically crystal hybrid magnetoresistance devives with high performance for next generation applications.

目前报道的有机复合磁电阻器件中有机半导体层主要是非晶态结构，有机层存在大量缺陷降低了载流子活性，并引起自旋翻转，导致了有机复合磁电阻现象多数在低温下观察到，室温磁电阻比值非常低。有机单晶具有结构上的有序性、高的载流子迁移率和良好的热稳定性等特性。本项目拟通过在磁性单晶衬底上生长特定晶体取向有机层（有机单晶或具有高度织构化多晶）半导体薄膜，研制在室温下具有高磁电阻比值的自旋电子学材料与器件。系统研究不同晶向有机材料与不同晶向磁性材料的相互作用和磁硬化等新物理现象，揭示磁性层/有机晶体层界面耦合的机理以及与晶体取向的内在联系。通过对不同器件中的自旋输运效应（GMR、TMR 等）的分析，理解自旋电子在特定晶体取向有机分子层中的输运特点、探索自旋电子在有机晶体层中注入或隧穿的高效通道和降低输运过程中自旋翻转的有效方法，为获得下一代高性能的有机晶体复合磁电阻器件提供理论和实验基础。

针对有机自旋电子器件中电子自旋易翻转，磁电阻低的问题，我们从电极、有机材料设计和器件制备等方面入手，采用实验制备与第一性原理计算相结合的方法对涉及的材料晶体取向生长、偶极作用和界面量子限域等开展了系统和有特色的研究，揭示了相关因素对磁性和电子自旋输运的影响及其物理机制。成功开发了以富勒烯、红荧烯、铁电聚合物和金属酞菁为传输层的系列有机复合磁电阻器件，实现了室温较高效率的自旋电子传输。主要成果包括：通过第一性原理计算发现Co（Fe）能带中X点的电子受到量子阱束缚引起了L10-MnGa/Co（Fe）磁耦合振荡；进一步研究发现，τ-MnAl/Co(Fe)的耦合限域与L10-MnGa/Co(Fe)不同，揭示了能隙受材料组分的强烈影响；在高效自旋阀器件制备中，通过引入AlO层有效降低了界面势垒和电导失配，提高了自旋传输效率，制备出了第一个室温铁电PVDF自旋阀器件；实现了室温最高磁电阻响应的rubrene自旋器件；第一次揭示了分子空间构型（C60和C70）对自旋电子传输的影响；实现了CuPc薄膜的取向生长；报道了第一个FePc自旋阀器件，对有机层中缺陷态对电子自旋传输的影响做了系统分析，区分了深陷阱和浅陷阱随测量温度和测量电压对自旋传输的影响。以上研究结果为开发新型有机自旋电子学器件积累了理论和实验经验。