Spin Injection into Graphene from Heusler Alloy Co_2MnGe (111) Surface: A First Principles Study

摘要

To obtain a larger spin signal for use in graphene-based spintronic devices, the spin injection efficiency needs to be enhanced. Previously researchers can increase the efficiency by inserting a tunnel barrier such as Al_2O_3 or MgO between ferromagnet and graphene. However, the key value in spin transport is still very low because of the conductance mismatch as well as the limit to fabricate a high-quality tunnel barrier at the junction surface. Here we use a highly spin-polarized ferromagnetic material--Heusler alloy Co2MnGe as a substitutional scheme without the tunnel barrier. The spin injection efficiency of our Co2MnGe (lll)/graphene junction can be as high as 73% which is much higher than 1% of ferromagnet/graphene or 30% of ferromagnet/ oxide/graphene using first-principles study. The large spin polarization can be explicated by analyzing the transmission spectrum at the nonequilibrium state.