Atomic-Scale Interfacial Magnetism in Fe/Graphene Heterojunction.

W Q Liu,Q M Zhang,C Lu,A Zhang,G Van Der Laan,Q X Li,R Zhang,Y B Xu,J J Wang,F Jin,W Y Wang,F Q Wang

doi:10.1038/srep11911

Abstract

Successful spin injection into graphene makes it a competitive contender in the race to become a key material for quantum computation, or the spin-operation-based data processing and sensing. Engineering ferromagnetic metal (FM)/graphene heterojunctions is one of the most promising avenues to realise it, however, their interface magnetism remains an open question up to this day. In any proposed FM/graphene spintronic devices, the best opportunity for spin transport could only be achieved where no magnetic dead layer exists at the FM/graphene interface. Here we present a comprehensive study of the epitaxial Fe/graphene interface by means of X-ray magnetic circular dichroism (XMCD) and density functional theory (DFT) calculations. The experiment has been performed using a specially designed FM1/FM2/graphene structure that to a large extent restores the realistic case of the proposed graphene-based transistors. We have quantitatively observed a reduced but still sizable magnetic moments of the epitaxial Fe ML on graphene, which is well resembled by simulations and can be attributed to the strong hybridization between the Fe 3dz2 and the C 2pz orbitals and the sp-orbital-like behavior of the Fe 3d electrons due to the presence of graphene.

Highlights

As a prototypical two-dimensional quantum system, graphene displays a combination of exceptional properties including large charge carrier mobility, high thermal conductivity, strong mechanical strength, excellent optical characteristics, electrically tuneable band gap, as well as the recently discovered long spin coherence length[1,2,3,4]
The X-ray magnetic circular dichroism (XMCD) was taken as the difference of the X-ray absorption (XAS) spectra, i.e., σ − − σ +, obtained by flipping the X-ray helicity at a fixed magnetic field of 3 T, under which the sample is fully magnetized with little paramagnetic contribution
The X-ray absorption (XAS) and XMCD of the Fe and Ni L2,3 absorption edges were performed and typical spectra obtained at 5–300 K are presented in Fig. 2a,b, respectively

Summary

Introduction

As a prototypical two-dimensional quantum system, graphene displays a combination of exceptional properties including large charge carrier mobility, high thermal conductivity, strong mechanical strength, excellent optical characteristics, electrically tuneable band gap, as well as the recently discovered long spin coherence length[1,2,3,4]. Graphene exhibits no signs of conventional spin-polarization and so far no experimental signature shows a ferromagnetic phase of graphene. This gap is filling up by combined efforts in multi-disciplinary research. Fascinating properties of spin transport phenomena were presented in the Co/graphene system[11,12], though theoretical calculations show that the atomic magnetic moment of Co can be reduced by more than 50% when absorbed on graphene surface[13]. In any proposed graphene-based transistors, the best opportunity for spin transport could only be achieved when no magnetic dead layer exists at the FM/graphene interface. Combined with the unique elemental selectivity of XMCD, such structure allows direct observation of the magnetization of FM2 at the FM2/ SC interface

Methods

Results

Conclusion