Magnetoresistance of vertical Co-graphene-NiFe junctions controlled by charge transfer and proximity-induced spin splitting in graphene

P U Asshoff,J L Sambricio,S Slizovskiy,I J Vera-Marun,A K Geim,A M Rakowski,A P Rooney,S J Haigh,A Mishchenko,E W Hill,V I Fal’Ko,I V Grigorieva

doi:10.1088/2053-1583/aa7452

P U Asshoff, J L Sambricio + Show 10 more

Open Access

https://doi.org/10.1088/2053-1583/aa7452

Copy DOI

Journal: 2D Materials	Publication Date: Jun 22, 2017
Citations: 82	License type: cc-by

Affiliation: University of Manchester, Henry Royce Institute

Abstract

Graphene is hailed as an ideal material for spintronics due to weak intrinsic spin–orbit interaction that facilitates lateral spin transport and tunability of its electronic properties, including a possibility to induce magnetism in graphene. Another promising application of graphene is related to its use as a spacer separating ferromagnetic metals (FMs) in vertical magnetoresistive devices, the most prominent class of spintronic devices widely used as magnetic sensors. In particular, few-layer graphene was predicted to act as a perfect spin filter. Here we show that the role of graphene in such devices (at least in the absence of epitaxial alignment between graphene and the FMs) is different and determined by proximity-induced spin splitting and charge transfer with adjacent ferromagnetic metals, making graphene a weak FM electrode rather than a spin filter. To this end, we report observations of magnetoresistance (MR) in vertical Co-graphene-NiFe junctions with 1–4 graphene layers separating the ferromagnets, and demonstrate that the dependence of the MR sign on the number of layers and its inversion at relatively small bias voltages is consistent with spin transport between weakly doped and differently spin-polarized layers of graphene. The proposed interpretation is supported by the observation of an MR sign reversal in biased Co-graphene-hBN-NiFe devices and by comprehensive structural characterization. Our results suggest a new architecture for vertical devices with electrically controlled MR.

Highlights

Please note that where the full-text provided on Manchester Research Explorer is the Author Accepted Manuscript or Proof version this may differ from the final Published version
Copyright and moral rights for the publications made accessible in the Research Explorer are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights
We report observations of magnetoresistance (MR) in vertical Co-graphene-NiFe junctions with 1 to 4 graphene layers separating the ferromagnets, and demonstrate that the dependence of the MR sign on the number of layers and its pte inversion at relatively small bias voltages is consistent with spin transport between weakly doped and differently spin-polarized layers of graphene

Summary

D Materials

Please note that where the full-text provided on Manchester Research Explorer is the Author Accepted Manuscript or Proof version this may differ from the final Published version. The most likely reason for this is that the reported FM-G-FM sandwiches (especially those fabricated by a combination of graphene transfer and deposition of FM films) were van der Waals us cri heterostructures [21,22] rather than truly lattice-matched crystals In this case, as we show below, graphene plays a different role, itself becoming a source of spin-polarized electrons due to the interplay of (i) its doping by charge transfer from the FM metal and (ii) proximity-induced spin splitting in graphene. (a similar approach was used in ref. [15], but our method is different in several important aspects, as described in

Methods and Supplementary

Findings

METHODS