Reducing the critical current for short-pulse spin-transfer switching of nanomagnets

We have fabricated permalloy/copper/permalloy nanopillar spin valves designed to reduce the critical current for spin-transfer switching while maintaining thermal stability of the free layer. Pulsed current amplitudes necessary for switching a 4.5-nm-thick permalloy free layer range from 0.4 mA for a 100 ns pulse to 2 mA for a 1 ns pulse, showing that the magnetization must be overdriven to achieve switching on short time scales. Comparisons to Landau-Lifshitz-Gilbert simulations indicate an effective damping parameter approximate to 0.03 and spin-torque efficiencies for parallel-to-antiparallel and antiparallel-to-parallel switching that are more symmetric than predicted by recent theoretical models. (c) 2005 American Institute of Physics.