Efficient Spin Injection into Graphene through a Tunnel Barrier: Overcoming the Spin-Conductance Mismatch

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.

Effective gating and tunable magnetic proximity effects in two-dimensional heterostructures

“…The significance of this choice is two-fold: (i) such systems include van der Waals (vdW) heterostructures with atomically sharp interfaces 16 which simplify the implementation of electrostatic gating, 2,17 (ii) these are key building blocks for graphene spintronics 18 with a prospect of gate-tunable magnetic proximity effects -an important precursor for lateral spin injection needed in many applications. 8,[19][20][21][22][23][24][25][26][27] This path to tunable magnetic proximity effects contradicts common expectations that a magnetic insulator is required to avoid a short-circuit effect of a metallic F. [28][29][30] In bulk materials the proximity-induced exchange splitting and magnetization decay over a much shorter distance compared to the spin-diffusion length, which is important for spin injection. 8 Consequently, the description of the spin injection usually completely neglects equilibrium proximity effects in the nonmagnetic materials.…”

Prospects of spintronics based on 2D materials

“…To overcome the above problems, Wu et al proposed to use hexagonal boron nitride ( h ‐BN), instead of oxide, as the tunnel barrier between graphene and the FM electrode . This is because h ‐BN has similar crystal structure and lattice constants as graphene.…”

Spin transport in fully hexagonal boron nitride encapsulated graphene

“…A 2D layer of thin hBN with close lattice match to graphene has been shown to exhibit pinhole-free tunneling characteristics [13,14]. It is also predicted to enhance the spin injection efficiency from a ferromagnet into graphene [15].…”