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

Abstract

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 0.4mA for a 100ns pulse to 2mA for a 1ns 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 ≈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.