Anisotropic Spin Relaxation Induced by Surface Spin-Orbit Effects

TL;DR

This paper reveals unexpected anisotropic spin relaxation in polycrystalline copper channels caused by surface spin-orbit effects, indicating new ways to control spin currents via polarization and gating.

Contribution

It demonstrates surface spin-orbit effects induce anisotropic spin relaxation in polycrystalline Cu, a novel insight into spin transport behavior.

Findings

Longer spin-relaxation length for spins parallel to the Cu channel

Surface spin-orbit effects explain the anisotropic relaxation

Potential for tunable spin current via polarization and gating

Abstract

It is a common perception that the transport of a spin current in polycrystalline metal is isotropic and independent of the polarization direction, even though spin current is a tensorlike quantity and its polarization direction is a key variable. We demonstrate surprising anisotropic spin relaxation in mesoscopic polycrystalline Cu channels in nonlocal spin valves. For directions in the substrate plane, the spin-relaxation length is longer for spins parallel to the Cu channel than for spins perpendicular to it, by as much as 9% at 10 K. Spin-orbit effects on the surfaces of Cu channels can account for this anisotropic spin relaxation. The finding suggests novel tunability of spin current, not only by its polarization direction but also by electrostatic gating.