Enhancement in spin-torque efficiency by nonuniform spin current generated within a tapered nanopillar spin valve

TL;DR

This paper demonstrates that nonuniform spin currents in tapered nanopillar spin valves can significantly improve spin-torque efficiency, leading to faster magnetic switching with lower currents, verified through simulations and experiments.

Contribution

It introduces a novel approach of using tapered geometries to generate nonuniform spin currents that enhance spin-torque efficiency and magnetic reversal performance.

Findings

Enhanced switching speed with smaller currents.

Experimental verification of efficiency improvements.

Tapered three-layer structures further reduce reversal times.

Abstract

We examine the effect a spatially non-uniform spin current with a component polarized partially out of the plane has on a low saturation magnetization nanomagnet free layer. Micromagnetic simulations indicate that the spin torque efficiency acting upon the reversing nanomagnet can be enhanced through this process, resulting in faster switching with smaller currents. In doing so, we determine that micromagnetic structure within the nanomagnets can be beneficial for reversal processes. We verify this enhancement experimentally in devices with a tapered nanopillar geometry that generates a spin current polarized partly out of plane. Finally, to take even better advantage of these effects, we examine micromagnetically the benefits of a tapered three-magnetic-layer structure that further reduces reversal times while maintaining the thermal stability of the free layer.