Effect of the low-resistance tunnel barriers induced inhomogeneous spin current distribution in graphene crossed configuration lateral spin valve

Yanping Liu,Junnan Ding,Juan Yu,Lingkai Cao,Zongwen Liu,Xiaofei Kuang,Yuanji Gao,Cheng Zeng,Jun He,Jiahong Zhong

doi:10.1063/1.5088200

Abstract

The nonlocal spin valve configuration consists of two ferromagnetic and nonmagnetic channels, which is an effective configuration for determining spin injection and accumulation. Here, we report that a reversed nonlocal spin signal was detected by changing the voltage probe configurations in graphene (Py/MgO/graphene/MgO/Py) lateral spin valves. The abnormal reversed spin-dependent nonlocal voltage is attributed to the nonuniform pinhole at the interface of the low-resistance tunnel barrier, which makes the charge current flow through the detection electrode and return to the graphene channel. We demonstrate that the channel-width induced spin-polarized current inhomogeneity significantly contributes to nonlocal resistance. A detailed description and simulated results of the tunnel junctions provide evidence for the reversal of the nonlocal voltage sign induced by the low-resistance tunnel barriers. Our work sheds light on the understanding of the spatial distribution of the spin current and the effect of the tunnel barrier, which are essential for the development of spintronic devices.

Highlights

Two-dimensional (2D) graphene with a single atomic layer has recently attracted much attention in spintronics because of its unique electronic transport properties.1–17 Graphene spintronics is of interest due to its high mobility and small spin-orbit interaction attributable to the carbon atoms with low atomic mass, whereby resulting in a long spin relaxation time10,18–24 and excellent spin transport properties
A comprehensive understanding of the spin dephasing during spin injection and the background signal induced by the spatial thickness distribution of oxide barriers remains missing
We investigated the spatial distribution of spin current in (Py/MgO/graphene/MgO/Py) lateral spin valves with various graphene widths and found that the spin signal strongly depends on the location of the voltage probe and the graphene width effects

Summary

Introduction

Two-dimensional (2D) graphene with a single atomic layer has recently attracted much attention in spintronics because of its unique electronic transport properties. Graphene spintronics is of interest due to its high mobility and small spin-orbit interaction attributable to the carbon atoms with low atomic mass, whereby resulting in a long spin relaxation time and excellent spin transport properties. Atomically thin oxide barrier MgO is a useful spin tunnel barrier material for spin injection from a ferromagnet (FM) into graphene.. The inhomogeneous spin current distribution in graphene nonlocal spin valve (NLSV) induced by width makes an indispensable contribution to the spin signal.. The inhomogeneous spin current distribution in graphene nonlocal spin valve (NLSV) induced by width makes an indispensable contribution to the spin signal.34–39 To clarify this phenomenon, in this work, we present a systematic investigation on the injection and detection of the spin current in a lateral ferromagneticMgO-graphene-MgO-ferromagnetic spin-valve device with a low resistance tunneling barrier interface. Our experimental and simulated results reveal that the inhomogeneous spin current distributions induced by the low-resistance tunnel barriers are responsible for the inverted spin signal behavior. Providing a deep understanding of the fundamental physics for spin accumulation in graphene is indispensable for the development of spintronic devices

Methods

Results

Conclusion