Current-driven magnetization reversal and spin-wave excitations in Co /Cu /Co pillars

Using thin film pillars approximately 100 nm in diameter, containing two Co layers of different thicknesses separated by a Cu spacer, we examine the process by which the scattering from the ferromagnetic layers of spin-polarized currents flowing perpendicular to the layers causes controlled reversal of the moment direction in the thin Co layer. The well-defined geometry permits a quantitative analysis of this spin-transfer effect, allowing tests of competing theories for the mechanism and also new insight concerning magnetic damping. When large magnetic fields are applied, the spin-polarized current no longer fully reverses the magnetic moment, but instead stimulates spin-wave excitations.