The bias dependence of spin injection in graphene lateral spin valves is systematically studied to determine the factors affecting the tunneling spin injection efficiency. Three types of junctions are investigated, including MgO and hexagonal boron nitride (hBN) tunnel barriers and direct contacts. A DC bias current applied to the injector electrode induces a strong nonlinear bias dependence of the nonlocal spin signal for both MgO and hBN tunnel barriers. Furthermore, this signal reverses its sign at a negative DC bias for both kinds of tunnel barriers. The analysis of the bias dependence for injector electrodes with a wide range of contact resistances suggests that the sign reversal correlates with bias voltage rather than current. We consider different mechanisms for nonlinear bias dependence and conclude that the energy-dependent spin-polarized electronic structure of the ferromagnetic electrodes, rather than the electrical field-induced spin drift effect or spin filtering effect of the tunnel barrier, is the most likely explanation of the experimental observations.
翻译:在石墨横向旋转阀门中,对旋转式喷气的偏向依赖性进行了系统研究,以确定影响旋转式喷气效率的因素。对三种类型的连接点进行了调查,包括MgO和六角正对亚硝酸盐隧道屏障和直接接触。对注射器电极应用的DC偏向性流使非局部旋转信号对磁极和 hBN隧道屏障都产生强烈的非线性偏向性依赖性。此外,这一信号将两种隧道屏障的负式DC偏向性信号反转。对具有广泛接触阻力的喷射器电极的偏向性依赖性分析表明,信号逆转与偏向电压相关,而不是与当前有关。我们考虑了非线性偏向依赖的不同机制,并得出结论,铁磁电极依赖的能量依赖性旋极电子结构,而不是由电场引发的旋转流效应或隧道屏障的旋转过滤效应,是实验观测的最可能的解释。