Magnetotransport through graphene spin valves

TL;DR

This paper theoretically investigates spin-dependent electron transport in graphene-based spin valves, revealing nonlinear current-voltage characteristics, zero-bias anomalies, and oscillatory TMR influenced by magnetic fields, temperature, and lead polarization.

Contribution

It introduces a comprehensive theoretical model for graphene spin valves considering arbitrary lead magnetization orientations and external magnetic fields, highlighting novel transport phenomena.

Findings

Nonlinear I-V curves without gate voltage.

Strong zero-bias TMR dip affected by lead polarization.

Periodic oscillations in conductance and TMR under magnetic fields.

Abstract

We present a theoretical study on the spin-dependent transport through a spin valve consisting of graphene sandwiched between two magnetic leads with an arbitrary orientation of the lead magnetization. No gate voltage is applied. Using Keldysh's nonequilibrium Green's function method we show that, in absence of external magnetic fields, the current-voltage curves are nonlinear. Around zero bias the differential conductance versus bias voltage possesses a strong dip. The zero-bias anomaly in the tunnel magnetoresistance (TMR) is affected strongly by the leads spin polarization. Depending on the value of the bias voltage TMR exhibits a behavior ranging from an insulating to a metallic-type. In presence of a static external magnetic field the differential conductance and TMR as a function of the bias voltage and the strength of the magnetic field show periodic oscillations due to Landau-level crossings. We also inspect the effects of the temperature and the polarization degrees on the differential conductance and TMR.