Efficient spin injection into graphene through a tunnel barrier: overcoming the spin conductance mismatch

TL;DR

This study uses first-principles calculations to demonstrate that an insulating h-BN barrier can significantly enhance spin injection efficiency from Ni into graphene by suppressing minority spin channels, addressing the conductance mismatch problem.

Contribution

The paper provides a detailed analysis of how different barriers affect spin injection efficiency, highlighting the effectiveness of h-BN as a tunnel barrier for graphene spintronics.

Findings

h-BN barrier greatly enhances spin injection efficiency

Cu and graphite barriers show low efficiency due to conductance mismatch

High efficiency is due to asymmetric effects on spin states

Abstract

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.