Research of spinterface in organic spintronic devices

Abstract

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>i.e.</i>, 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.