Theoretical Study of Spintronics Devices Based on Two-Dimensional Materials

采用第一性原理研究了自旋轨道耦合（SOC）对石墨烯（Gr）和镍（Ni）界面的影响。由于荷电性，当Ni原子远离界面时，其磁化方向与界面平行。当它们向界面移动时，它们开始沿垂直于界面的方向旋转，直到它们在界面处具有完全垂直磁化。这种旋转是由于与Gr的杂化降低了面内轨道矩，使界面处的面外轨道矩更强。这一结果也适用于六方氮化硼(hBN)/Ni界面。在Ni/Gr/Ni器件和Ni/hBN-Gr-hBN/Ni器件中，该效应不影响石墨烯的可控狄拉克锥，显示了自旋阀器件在Gr上控制平面内自旋电流的有效性。同时，我们发现当Gr/Ni中的C原子与金属配合物中的金属原子杂化并对金属配合物产生机械扰动时，其磁矩会引起自旋翻转机制。这种自旋翻转的发生是因为在靠近费米能量的自旋多数通道中的C原子的态密度由于键强度的变化而从低于费米能量的能级移动到高于费米能量的能级，从而减少了自旋多数通道中的电子占比。该机制可用于石墨烯狄拉克锥的局部控制，微调石墨烯的面内电导。

A first-principles study was done to look at the effect of spin-orbit coupling (SOC) on the interface between graphene (Gr) and nickel (Ni). Due to SOC, when Ni atoms were far from the interface, they were magnetized in a parallel direction to the interface. As they move toward the interface, they begin to rotate in a direction perpendicular to the interface until they have full perpendicular magnetization at the interface. This rotation is caused by the fact that hybridization with Gr reduces the in-plane orbital moment and makes the out-of-plane orbital moment stronger at the interface. This result was also applied to the hexagonal Boron Nitride (hBN)/Ni interface. Further, it was confirmed that this effect does not affect the controllable Dirac cone of graphene in the proposed Ni/Gr/Ni as well as Ni/hBN-Gr-hBN/Ni device, showing the effectiveness of controlling in-plane spin-current on Gr for the spin-valve device.Parallelly, we found a spin-flipping mechanism that can be initiated on the induced magnetic moment of C atoms in Gr/Ni when it hybridizes with a metal atom of the metal complex and a mechanical disturbance is made to the metal complex. This spin-flipping happens because the density of states of C atoms in the spin-majority channel near Fermi energy moves from energy levels below Fermi energy to energy levels above Fermi energy due to changes in the strength of the bonds, reducing the electron population in the spin-majority channel. This mechanism can be used for local control of the graphene Dirac cone, fine-tuning the in-plane conductance of graphene.