Time-Resolved Spin-Torque Switching and Enhanced Damping in Permalloy/Cu/Permalloy Spin-Valve Nanopillars

We report time-resolved measurements of current-induced reversal of a free magnetic layer in Permalloy/Cu/Permalloy elliptical nanopillars at temperatures $T=4.2\mathrm{K}$ to 160 K. Comparison of the data to Landau-Lifshitz-Gilbert macrospin simulations of the free layer switching yields numerical values for the spin torque and the Gilbert damping parameters as functions of $T$. The damping is strongly $T$ dependent, which we attribute to the presence of an antiferromagnetic oxide layer around the perimeter of the Permalloy free layer. This adventitious antiferromagnetic oxide can have a major impact on spin-torque phenomena.