Tunneling Magnetoresistance Effect Graphene Based Magnetotunnel Junctions

As a two dimension nano-material, graphene is regarded as important materials for nanoelectronics and spintronics devices due to its superior electronic properties.One of the most important topic in spintronics is how to obtain high spin-polarized current. In this paper, using ab initio calculations and non-equilibrium Green’s function method, we study spin transport properties of the magnetotunnel junction based on graphene, the conclusions are as follows:1、We systematically study the effect of Cr-graphene planar junction on the transport properties of graphene. The electronic transport properties of Cr/graphene/Cr are greatly improved due to the strong coupling between carbon and Cr atoms of the magnetotunnel junction. At the zero bias, the tunneling magnetresistance ratio based on such magnetotunnel junctions reaches 108%, which is close to the perfect spin filter. The interaction between the graphene sheet and Cr produces a band gap for graphene and the graphene is n-type doped by the electrodes.Moreover, the electronic transport of the system will occur around the high symmetry M and K points in reciprocal space, and there is large k|-resolved transmission conductance of spin up transmission in Cr(111) system around M and K points.Meanwhile, we calculate the transmission conductance and tunneling magnetresistance under external bias. Results indicate that the tunneling magnetresistance of the system is dependent on the external bias. Interestingly, the TMR ratio reduces in the bias window of [-0.5 V, 0.2 V], however, when the bias is larger than 0.2 V, the TMR ratio shows a 65% platform under positive bias. This feature is markedly different from that of conventional MgO-based MTJs where TMR drops with the increase in bias. The stable TMR ratio under external bias of Cr/graphene/Cr shows potential in spintronics;2、We study the electronic transmission properties of the Ni/graphene/Ni and Ni/graphane/Ni tunneling magnetresistance junction. When graphane adsorbs on the Ni surface of the direction(111), top-fcc is the most stable configuration. By analyzing the spin transmission spectra, we find that the magnetresistance ratio of Ni/graphane/Ni magnetotunnel junctions is reduce 6.4 percent than that of Ni/graphene/Ni magnetotunnel junctions, beacause of the selectivity makes graphene an effective tunneling channel in Ni/graphene/Ni system. Moreover, hydrogenated caneffectively regulate the work function of graphene/Ni planar junction, and the work function will affect the TMR value of the system.