Magnetoresistance in graphene-based ferromagnetic/ferromagnetic barrier/superconductor junction

Abstract

We study the magnetoresistance (MR) and spin transport in a graphene-based ferromagnetic/ferromagnetic barrier/s-wave superconductor (FF BS) junction for two regimes including retro-Andreev reflection (AR) (E F =100Δ 0) and retroreflection crossing over to specular Andreev reflection (E F=Δ 0). We observed that the variation of exchange energy in the ferromagnetic region h 1 has a stronger effect on the amplitude of the MR oscillations rather than length, exchange energy, and effective gate potential in the F B region in both regimes. In the E F =100Δ 0 regime, the higher values of exchange energy h 1 approach E F, which decrease the amplitude of the MR oscillations with respect to F B length. By increasing the exchange energy up to h 1>E F, a phase shift occurs for the peaks of the MR curves and the amplitude of the MR oscillations reaches its maximum value at the exchange energy h c =2E F+U 0. Furthermore, in the E F =100Δ 0 regime, at the exchange energy h 1=eV, the amplitude of the MR oscillations approaches its maximum value. At this value of energy of carriers eV +h 1 - E F (Dirac point), the sign of the energy will be reversed and a transition from the retroreflection to the specular Andreev reflection occurs. Thus, in this regime (E F =100Δ 0), by observing the maximum of the MR at specified values of eV and h 1, we can measure the Fermi energy of the graphene. While in the E F =100Δ 0 regime, the MR versus bias energy can be tuned from the positive to negative values by varying h 1, but in the E F =100Δ 0 regime, the MR shows only the positive values. In addition, we have investigated the spin conductance in both regimes. © 2012 American Institute of Physics.