  The spin filter capability of a (0,8) armchair graphene nanoribbon with Fe
atoms at substitutional sites is investigated by density functional theory in
combination with the non-equilibrium Greens function technique. For specific
arrangements, a high degree of spin polarization is achieved. These include a
single substitution at an edge position or double substitution in the central
sector of the transmission element. The possibility of switching between
majority and minority spin polarization by changing the double substitution
geometry is predicted. Including the bias dependence of the transmission
function proves to be essential for correct representation of the spin-resolved
current-voltage profiles.
