Department of Physics, Michigan Technological University, Houghton, Michigan 49931, United States.
ACS Nano. 2012 Apr 24;6(4):3580-8. doi: 10.1021/nn3006569. Epub 2012 Mar 15.
The observations of both positive and negative signs in tunneling magnetoresistance (TMR) for the same organic spin-valve structure have baffled researchers working in organic spintronics. In this article, we provide an answer to this puzzle by exploring the role of metal-molecule interface on TMR in a single molecular spin-valve junction. A planar organic molecule sandwiched between two nickel electrodes is used to build a prototypical spin-valve junction. A parameter-free, single-particle Green's function approach in conjunction with a posteriori, spin-unrestricted density functional theory involving a hybrid orbital-dependent functional is used to calculate the spin-polarized current. The effect of external bias is explicitly included to investigate the spin-valve behavior. Our calculations show that only a small change in the interfacial distance at the metal-molecule junction can alter the sign of the TMR from a positive to a negative value. By changing the interfacial distance by 3%, the number of participating eigenchannels as well as their orbital characteristics changes for the antiparallel configuration, leading to the sign reversal in TMR.
对于相同的有机自旋阀结构，隧穿磁电阻（TMR）出现正、负两种信号的观察结果令从事有机自旋电子学研究的人员感到困惑。在本文中，我们通过研究单个分子自旋阀结中金属-分子界面对 TMR 的作用，为这个难题提供了答案。我们使用夹在两个镍电极之间的平面有机分子来构建原型自旋阀结。我们采用无参数、单粒子格林函数方法，结合后验、自旋无限制密度泛函理论，其中涉及混合轨道相关函数，来计算自旋极化电流。我们明确包括外部偏压的影响，以研究自旋阀的行为。我们的计算表明，金属-分子结的界面距离只需稍有变化，TMR 的符号就可以从正变为负。通过将界面距离改变 3%，对于反平行配置，参与的本征态数量及其轨道特性发生变化，导致 TMR 的符号反转。
