Employing first-principles calculations, we investigate the efficiency of spin injection from a ferromagnetic electrode (Ni) into graphene and a 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 $\mathrm{Ni}/\text{barrier}/\text{graphene}$ junction is 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 $\mathrm{Ni}/\mathrm{Cu}/\text{graphene}$ and $\mathrm{Ni}/\text{graphite}/\text{graphene}$ junctions are low, due to the spin-conductance mismatch. Further examination of 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.

• Received 30 May 2014

DOI:https://doi.org/10.1103/PhysRevApplied.2.044008

Source: http://link.aps.org/doi/10.1103/PhysRevApplied.2.044008