Spin transfer in asymmetric Co/Cu/Co bilayer magnetic nanopillars junctions has been studied at low temperature as a function of free-layer thickness. The phase diagram for current-induced magnetic excitations has been determined for magnetic fields up to 7.5 T applied perpendicular to the junction surface and free-layers thicknesses from 2 to 5 nm. The junction magnetoresistance is independent of thickness. The critical current for magnetic excitations decreases linearly with decreasing free-layer thickness, but extrapolates to a finite critical current in the limit of zero thickness. The limiting current is in quantitative agreement with that expected due to a spin-pumping contribution to the magnetization damping. It may also be indicative of a decrease in the spin-transfer torque efficiency in ultrathin magnetic layers.
@article{arxiv.cond-mat/0602159,
title = {Spin-transfer in bilayer magnetic nanopillars at high fields as a function of free layer thickness},
author = {W. Chen and A. D. Kent and M. J. Rooks and N. Ruiz and J. Z. Sun},
journal= {arXiv preprint arXiv:cond-mat/0602159},
year = {2007}
}