Electrical spin injection from ferromagnetic metals into graphene is hindered by the impedance mismatch between the two materials. This problem can be reduced by the introduction of a thin tunnel barrier at the interface. We present room temperature non-local spin valve measurements in cobalt/aluminum-oxide/graphene structures with an injection efficiency as high as 25%, where electrical contact is achieved through relatively transparent pinholes in the oxide. This value is further enhanced to 43% by applying a DC current bias on the injector electrodes, that causes carrier drift away from the contact. A reverse bias reduces the AC spin valve signal to zero or negative values. We introduce a model that quantitatively predicts the behavior of the spin accumulation in the graphene under such circumstances, showing a good agreement with our measurements.
@article{arxiv.0811.2960,
title = {Controlling the efficiency of spin injection into graphene by carrier drift},
author = {C. Józsa and M. Popinciuc and N. Tombros and H. T. Jonkman and B. J. van Wees},
journal= {arXiv preprint arXiv:0811.2960},
year = {2009}
}