2D Materials and Devices for Spintronics: First-Principles Studies

The key to success of spintronics is identification of suitable materials and evaluation of their performance in devices. While experimental studies take time and require a lot of resources, computational study, particularly first-principles calculations, is playing an important role. We have been using such methods to investigate a series of materials as well as conceptual design of spintronic devices. In earlier studies, [1], [2] we proposed spin logic gates based on zigzag graphene nanoribbons. However, some issues still remain for graphene based spintronic devices, and one of them is the low efficiency of spin-injection from a metal lead to graphene. Through first-principles calculations, we found that spin injection efficiency from a metal lead to graphene can be enhanced by using a hexagonal boron nitride (h-BN) between the electrode and graphene. [3] We also investigated transport property of phospherene nanoribbons (PNRs). In contrast to graphene and MoS2 nanoribbons, the carrier transport channels under low bias are mainly located in the interior of both armchair and zigzag PNRs, and immune to small amounts of edge defects. High on/off ratio dual-gate FET can be achieved using PNRs. [4] Our recent calculations reveal that phospherene can be made magnetic by an interplay of vacancy and strain, even though neither P vacancy nor external strain alone results in magnetism in phosphorene. When either a biaxial strain or a uniaxial strain along the zigzag direction of phosphorene containing P vacancies reaches 4%, the system favours a spin-polarized state with a magnetic moment of 1 $\mu_{\mathrm{B}}$ per vacancy site. [5]