Spin-polarization And Magnetoresistance In Graphene-based Resonant-tunnelling Structures

In this paper, ferromagnet/graphene-based double barriers (wells)/ferromagnet resonant tunnelling structures are designed, the spin-polarized transport of relativistic electrons and tunnel magnetoresistance (TMR) are investigated with the transfer matrix method. The main conclusions are as follows:We callulated the spin-dependent transmission coefficient and the conductance in the FG/IG/G/IG/FG structure by using transfer-matrix method. The numrical results indicated that the spin-polarization can be modified not only by the barrier (well) heights (depths) but also by the electron incident angle in the case of certain condition.Firstly, not only the spin-up state electrons but also the spin-down state electrons show the anisotropic Klein tunnelling effect in the double barrier junction. The barrier always remains perfectly transparent for angles close to normal incidence, and the spin-polarization is suppressed completely. Transmission for spin-down electrons is smoother than that for spin-up electrons, which is more complex and includes more resonant peaks. In the double barrier junction, with increasing well widthg, more resonant peaks appear of the transmission coefficient.Secondly, some features for the double well junction are similar to the double barrier model. The main difference is that perfect tunnelling of the transmission for spin-down state electrons only occurs for angles close to normal incidence but with a strong enhancement of the perfect transmission regions. For the spin-up state electrons, resonant peaks appear for large incident angles as well as at normal incidence.Thirdly, the conductance shows oscillation characteristics in the double barrier junction with the increase of the potential profile. When the Fermi energy is large enough, the difference in the conductance of parallel and antiparallel magnetization configurations for the two ferromagnetic electrodes becomes smaller, which is qualitatively different from the case of normal, non-relativistic spin-polarized electrons.At last, the conductance oscillates and the amplitude becomes smaller with with varying inter-well separation in the double barrier junction. Compared with the double barrier model, the value of the conductance for the double well junction is larger.