Time-Resolved Spin Torque Switching and Enhanced Damping in Py/Cu/Py   Spin-Valve Nanopillars
  We report time-resolved measurements of current-induced reversal of a free magnetic layer in Py/Cu/Py elliptical nanopillars at temperatures T = 4.2 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 antiferromagnetic pinning behavior of a thin permalloy oxide layer around the perimeter of the free layer. This adventitious antiferromagnetic pinning layer can have a major impact on spin torque phenomena. 
N. C. Emley, I. N. Krivorotov, A. G. F. Garcia, O. Ozatay, J. C.   Sankey, D. C. Ralph and R. A. Buhrman