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

We examine the effect that a spatially nonuniform 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 experimentally verify this enhancement in devices with a tapered nanopillar geometry that generates a spin current polarized partially out of plane.