Fig. 7. Spin-dependent band calculations for complete spin valve stacks.

Strikingly, when a both Ni and Co are in contact with graphene, the spin polarization of graphene can be reversed and becomes positive. The amplitude of the spin polarization seems to depend on the extent of FM/Gr hybridization, with a strong increase b in the case of strong interaction with Co. This reveals that the spin polarization of graphene in Ni/Gr/Co cannot be simply derived from the spin polarization of graphene in Ni/Gr and Co/Gr. c Electronic band structure of Ni/Gr/Co junction for (blue) majority and (red) minority electronic bands are displayed. Blue and red dots correspond to the projection of the majority and minority Hamiltonian eigenstates on carbon atoms. The size of the dot is proportional to the amplitude of the projection, i.e. the “carbon” character of the eigenstate. For majority carriers, the Dirac cone structure is shifted and a gap is opened. In contrast, for minority carriers, the Dirac cone structure has completely vanished due to hybridization. A strong spin asymmetry has been induced by proximity effect.