Controlling the efficiency of spin injection into graphene by carrier drift

TL;DR

This paper demonstrates that applying a DC current bias to graphene spin injectors significantly enhances spin injection efficiency by carrier drift, supported by experimental measurements and a predictive model.

Contribution

It introduces a model predicting spin accumulation behavior under bias and shows how carrier drift can boost spin injection efficiency in graphene.

Findings

Spin injection efficiency reaches 25% with transparent pinholes.

Applying DC bias increases efficiency to 43%.

Reverse bias suppresses the spin signal.

Abstract

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.