Magnetoresistance and negative differential resistance in Ni/graphene/Ni vertical heterostructures driven by finite bias voltage: A first-principles study

Abstract

Using the nonequilibrium Green's function formalism combined with density functional theory, we study finite bias quantum transport in Ni/Gr${}_{n}/$Ni vertical heterostructures where $n$ graphene layers are sandwiched between two semi-infinite Ni(111) electrodes. We find that the recently predicted ``pessimistic'' magnetoresistance of 100$%$ for $n\ensuremath{\ge}5$ junctions at zero bias voltage ${V}_{b}\ensuremath{\rightarrow}0$ persists up to ${V}_{b}\ensuremath{\simeq}0.4$ V, which makes such devices promising for spin-torque-based device applications. In addition, for parallel orientations of the Ni magnetizations, the $n=5$ junction exhibits a pronounced negative differential resistance as the bias voltage is increased from ${V}_{b}=0$ V to ${V}_{b}\ensuremath{\simeq}0.5$ V. We confirm that both of these nonequilibrium transport effects hold for different types of bonding of Gr on the Ni(111) surface while maintaining Bernal stacking between individual Gr layers.