Impact of tunnel barrier strength on magnetoresistance in carbon nanotubes

TL;DR

This study explores how the strength of the tunnel barrier influences magnetoresistance in carbon nanotube spin valves, revealing a complex relationship and consistent spin lifetime measurements with other spintronic materials.

Contribution

It demonstrates the significant impact of tunnel barrier strength on magnetoresistance and provides a detailed model of this dependence using scattering matrix approach.

Findings

Magnetoresistance depends non-trivially on tunnel barrier strength.

Spin lifetime in nanotubes is approximately 1.1 ns.

Tunneling magnetoresistance is confirmed as the primary mechanism.

Abstract

We investigate magnetoresistance in spin valves involving CoPd-contacted carbon nanotubes. Both temperature and bias voltage dependence clearly indicate tunneling magnetoresistance as the origin. We show that this effect is significantly affected by the tunnel barrier strength, which appears to be one reason for the variation between devices previously detected in similar structures. Modeling the data by means of the scattering matrix approach, we find a non-trivial dependence of the magnetoresistance on the barrier strength. Furthermore, analysis of the spin precession observed in a nonlocal Hanle measurement yields a spin lifetime of $\tau_s = 1.1\,$ns, a value comparable with those found in silicon- or graphene-based spin valve devices.