Employing first-principles calculations, we investigate efficiency of spin injection from a ferromagnetic (FM) electrode (Ni) into graphene and possible enhancement by using a barrier between the electrode and graphene. Three types of barriers, h-BN, Cu(111), and graphite, of various thickness (0-3 layers) are considered and the electrically biased conductance of the Ni/Barrier/Graphene junction are calculated. It is found that the minority spin transport channel of graphene can be strongly suppressed by the insulating h-BN barrier, resulting in a high spin injection efficiency. On the other hand, the calculated spin injection efficiencies of Ni/Cu/Graphene and Ni/Graphite/Graphene junctions are low, due to the spin conductance mismatch. Further examination on the electronic structure of the system reveals that the high spin injection efficiency in the presence of a tunnel barrier is due to its asymmetric effects on the two spin states of graphene.
@article{arxiv.1411.0779,
title = {Efficient spin injection into graphene through a tunnel barrier: overcoming the spin conductance mismatch},
author = {Qingyun Wu and Lei Shen and Zhaoqiang Bai and Minggang Zeng and Ming Yang and Zhigao Huang and Yuan Ping Feng},
journal= {arXiv preprint arXiv:1411.0779},
year = {2014}
}