Current-induced excitations in single cobalt ferromagnetic layer nanopillars

Current-induced excitations in Cu/Co/Cu single ferromagnetic layer nanopillars ( approximately 50 nm in diameter) have been studied experimentally as a function of Co layer thickness at low temperatures for large applied fields perpendicular to the layers. For asymmetric junctions current-induced excitations are observed at high current densities for only one polarity of the current and are absent at the same current densities in symmetric junctions. These observations confirm recent predictions of spin-transfer torque induced spin-wave excitations in single layer junctions with a strong asymmetry in the spin accumulation in the leads.