Study On Rectification Characteristics Of Organic Spin Diodes

As a new branch of spintronics, organic spintronics has attracted more and more attention in recent years, which mainly investigates spin creation and annihilation, electron spin injection, spin-dependent transport and builds functional devices. Organic materials such as single molecules, polymers and organic single crystals are usually cheap, low-weight, and can be synthesized in large area with chemical methods. In addition, organic materials are so soft that it can form a stable interface with other metal easily. What’s more, the very long spin relaxation time due to the weak spin-orbit and hyperfine interactions in an organic material make organic materials become easy to realize spin-dependent transport.In recent years, several designs of organic ferromagnetic device have been proposed theoretically and demonstrated experimentally. Generally, there are two kinds of organic spintronic devices involved to now:one is to use nonmagnetic molecules sandwiched between two magnetic electrodes, i.e., organic spin valves, which realizes its function through the nondegenerate spin freedom degree of electrodes. And its resistance is modulated by an applied magnetic field; the other is to choose organic magnetic molecules as the central medium, where the spintronic functions are designed based on the intrinsic property of the magnetic molecules, such as spin filtering and spin-current rectification and so on.This paper is based on metal/organic ferromagnetic/metal sandwich structure. We take organic magnetic polymer poly-BIPO as the interlayer. Use the method of SSH model coupled with Green’s function, we investigated the effect of excited states and interfacial coupling on the organic spin rectifier separately:1. The results demonstrate that the structural asymmetry of the co-oligomer is modulated by the spin excited states, which is embodied in the wave functions of the eigenstates as well as the spin density wave. By calculating the transport property, a robust spin-current rectification concomitant with a charge-current rectification is observed in all spin excited states. However, the current through the diode is suppressed distinctly by the spin excited states, while the rectification ratios may be reduced or enhanced depending on the bias and the excited spins.2. In the case of spin-independent coupling, the rectification ratio firstly grows up and then diminishes with interfacial coupling strength and there is a inflection point. An optimal interfacial coupling strength with significant enhanced rectification ratio is found, whose value depends on the structural asymmetry of the molecule. In the case of spin-resolved coupling, we found that only the variation of the interfacial coupling with specific spin is effective to modulate the rectification, where its modulation for the charge-current rectification and spin-current rectification are opposite. A transition of the spin-current rectification between parallel spin-current rectification and antiparallel spin-current rectification may be observed at some specific spin-resolved interfacial couplings.