Measuring anisotropic spin relaxation in graphene

TL;DR

This paper compares methods to measure anisotropic spin relaxation in graphene, introducing a numerical simulation for data fitting, and finds a small but distinct anisotropy influenced by multiple relaxation mechanisms.

Contribution

It presents a comprehensive comparison of measurement techniques and introduces a numerical simulation to accurately analyze anisotropic spin relaxation in graphene.

Findings

Small but distinct spin relaxation anisotropy detected

In-plane/out-of-plane Hanle method identified as most reliable

Multiple relaxation mechanisms, including Rashba spin-orbit, contribute to anisotropy

Abstract

We compare different methods to measure the anisotropy of the spin-lifetime in graphene. In addition to out-of-plane rotation of the ferromagnetic electrodes and oblique spin precession, we present a Hanle experiment where the electron spins precess around either a magnetic field perpendicular to the graphene plane or around an in-plane field. In the latter case, electrons are subject to both in-plane and out-of-plane spin relaxation. To fit the data, we use a numerical simulation that can calculate precession with anisotropies in the spin-lifetimes under magnetic fields in any direction. Our data show a small, but distinct anisotropy that can be explained by the combined action of isotropic mechanisms, such as relaxation by the contacts and resonant scattering by magnetic impurities, and an anisotropic Rashba spin-orbit based mechanism. We also assess potential sources of error in all three types of experiment and conclude that the in-plane/out-of-plane Hanle method is most reliable.