Impurity-induced spin gap asymmetry in nanoscale graphene

We present a way to control both the band gap and the magnetic properties of nanoscale graphene, which might prove highly beneficial for application in nanoelectronic and spintronic devices. We have shown that chemical doping by nitrogen along a single zigzag edge lowers the symmetry from D(2h) (pure graphene) to C(2 nu), thereby accommodating the state with antiferromagnetic spin ordering of localized states between the zigzag edges. This leads to an increase in the gap in comparison to that of pure graphene in its highest possible symmetry of D(2h) and a shift of the molecular orbitals localized on the doped edge in such a way that the spin gap asymmetry, which can lead to half metallicity under certain conditions, is obtained. The doping in the middle of the graphene layer along the zigzag edge results in an impurity level between the highest occupied molecular orbital and lowest unoccupied molecular orbital of pure graphene (much like in semiconductor systems) thus decreasing the band gap and adding unpaired electrons, which can also be used to control the graphene conductivity.