Bias induced up to 100% spin-injection and detection polarizations in ferromagnet/bilayer-hBN/graphene/hBN heterostructures

M Gurram,B J Van Wees,S Omar

doi:10.1038/s41467-017-00317-w

Abstract

We study spin transport in a fully hBN encapsulated monolayer-graphene van der Waals heterostructure at room temperature. A top-layer of bilayer-hBN is used as a tunnel barrier for spin-injection and detection in graphene with ferromagnetic cobalt electrodes. We report surprisingly large and bias-induced (differential) spin-injection (detection) polarizations up to 50% (135%) at a positive voltage bias of + 0.6 V, as well as sign inverted polarizations up to −70% (−60%) at a reverse bias of −0.4 V. This demonstrates the potential of bilayer-hBN tunnel barriers for practical graphene spintronics applications. With such enhanced spin-injection and detection polarizations, we report a record two-terminal (inverted) spin-valve signals up to 800 Ω with a magnetoresistance ratio of 2.7%, and achieve spin accumulations up to 4.1 meV. We propose how these numbers can be increased further, for future technologically relevant graphene based spintronic devices.

Highlights

We study spin transport in a fully hexagonal boron nitride (hBN) encapsulated monolayer-graphene van der Waals heterostructure at room temperature
In order to explore the potential of hBN tunnel barriers for graphene spin valve devices, one can study the role of current/ voltage bias for spin-injection and detection with FM electrodes
Recent first-principles calculations of the proximity exchange coupling induced in graphene by Zollner et al.[12] have predicted that an applied electric field in Co/hBN/graphene system can reverse the sign of the proximity-effect-induced equilibrium spin polarization in graphene

Summary

Introduction

We study spin transport in a fully hBN encapsulated monolayer-graphene van der Waals heterostructure at room temperature. We report surprisingly large and bias-induced (differential) spin-injection (detection) polarizations up to 50% (135%) at a positive voltage bias of + 0.6 V, as well as sign inverted polarizations up to −70% (−60%) at a reverse bias of −0.4 V This demonstrates the potential of bilayer-hBN tunnel barriers for practical graphene spintronics applications. With such enhanced spininjection and detection polarizations, we report a record two-terminal (inverted) spin-valve signals up to 800 Ω with a magnetoresistance ratio of 2.7%, and achieve spin accumulations up to 4.1 meV. We propose how these numbers can be increased further, for future technologically relevant graphene based spintronic devices. We demonstrate a two-terminal (inverted) spin-valve with a record magnitude of the spin signal reaching 800 Ω with magnetoresistance ratio of 2.7%

Methods

Results

Conclusion