Magnetization reversal driven by spin-polarized current in exchange-biased nanoscale spin valves

We report micromagnetic simulations of current-driven magnetization reversal of the free-layer nanomagnet in Ir20Mn80/Ni80Fe20/Cu/Ni80Fe20 nanoscale spin valves for large current pulses and compare the results to experiments. Our simulations demonstrate that the mechanism of current-driven magnetization reversal in these samples can depend strongly on the equilibrium angle between the magnetizations of the pinned layer and the free layer of the spin valve. In the case of collinear equilibrium magnetizations, the reversal proceeds via nucleation of a vortex. However, even small misalignments of the magnetizations of the free and the pinned layers, on the order of 5 degrees-10 degrees, can result in magnetization reversal by a macrospinlike coherent precessional rotation. This result is in good agreement with recent experimental observations.