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中国物理学会期刊

有机自旋电子器件中的自旋界面研究进展

CSTR: 32037.14.aps.71.20211786

Research of spinterface in organic spintronic devices

CSTR: 32037.14.aps.71.20211786
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  • 自旋器件有望实现量子信息存储、传感和计算, 是下一代数据存储和通信的理想器件. 与无机自旋器件相比, 有机自旋器件不仅可以实现传统无机自旋器件的功能, 而且在同一有机自旋阀器件中会同时测到正负磁电阻信号, 这是因为有机分子与铁磁电极在界面会发生自旋杂化而产生独特的自旋界面. 通过控制自旋界面, 可以改变界面处分子能级展宽和偏移程度, 从而实现对磁电阻信号的可控调制. 有机自旋阀器件发展迅速, 但仍有一些问题亟待研究, 如对自旋界面进行识别和表征, 以及利用自旋界面对有机自旋阀信号进行操控等. 针对上述问题, 本文首先综述了有机自旋阀的基本原理, 通过对比无机有机材料能级结构的差异解释了有机自旋阀中自旋界面形成的原因, 对于有机自旋阀中磁电阻信号的增强和反转现象, 利用自旋界面模型中能级展宽和偏移进行了解释; 接着列举了自旋界面的实验识别案例, 如利用对表面敏感的表征技术对自旋界面进行识别以及设计新颖的器件结构验证自旋界面的存在等; 然后汇总了利用自旋界面调制自旋信号的相关工作, 自旋界面的调制可以通过电场调节铁电层的铁电极化、诱导铁磁电极相变、界面化学工程和磁交换相互作用等方式实现; 最后总结了有机自旋界面中仍需解决的问题, 并对有机自旋界面的识别和可控利用进行了展望.

     

    Spintronics are attractive to the utilization in next-generation quantum-computing and memory. Compared with inorganic spintronics, organic spintronics not only controls the spin degree-of-freedom but also possesses advantages such as chemical tailorability, flexibility, and low-cost fabrication process. Besides, the organic spin valve with a sandwich configuration that is composed of two ferromagnetic electrodes and an organic space layer is one of the classical devices in organic spintronics. Greatly enhanced or inversed magnetoresistance (MR) sign appearing in organic spin valve is induced by the unique interfacial effect an organic semiconductor/ferromagnetic interface. The significant enhancement or inversion of MR is later proved to be caused by the spin-dependent hybridization between molecular and ferromagnetic interface, i.e., the spinterface. The hybridization is ascribed to spin-dependent broadening and shifting of molecular orbitals. The spinterface takes place at one molecular layer when attaching to the surface of ferromagnetic metal. It indicates that the MR response can be modulated artificially in a specific device by converting the nature of spinterface. Despite lots of researches aiming at exploring the mechanism of spinterface, several questions need urgently to be resolved. For instance, the spin polarization, which is difficult to identify and observe with the surface sensitive technique and the inversion or enhancement of MR signal, which is also hard to explain accurately. The solid evidence of spinterface existing in real spintronic device also needs to be further testified. Besides, the precise manipulation of the MR sign by changing the nature of spinterface is quite difficult. According to the above background, this review summarizes the advance in spinterface and prospects future controllable utilization of spinterface. In Section 2, we introduce the basic principle of spintronic device and spinterface. The formation of unique spinterface in organic spin valve is clarified by using the difference in energy level alignment between inorganic and organic materials. Enhancement and inversion of MR sign are related to the broadening and shifting of the molecular level. In Section 3, several examples about identification of spinterface are listed, containing characterization by surface sensitive techniques and identification in real working devices. In Section 4 some methods about the manipulation of spinterface are exhibited, including modulation of ferroelectric organic barrier, interface engineering, regulation of electronic phase separation in ferromagnetic electrodes, etc. Finally, in this review some unresolved questions in spintronics are given, such as multi-functional and room-temperature organic spin valve and improvement of the spin injection efficiency. Spinterface is of great importance for both scientific research and future industrial interest in organic spintronics. The present study paves the way for the further development of novel excellent organic spin valves.

     

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