This study investigates current-driven magnetization reversal and spin wave excitations in Co/Cu/Co pillars. Using pillars with diameters of ~100 nm and two Co layers of different thicknesses separated by a Cu spacer, the researchers examine the effects of spin-polarized currents flowing perpendicular to the layers. According to spin-transfer theory, spin-polarized electrons flowing from the thin to the thick Co layer can switch the magnetic moments of the layers to an antiparallel state, while a reversed current causes switching to a parallel state. When large magnetic fields are applied, the current no longer fully reverses the magnetic moment but instead stimulates spin-wave excitations. Theoretical calculations suggest that spin-polarized currents can exert a torque on the magnetic moment of a conductor, potentially flipping the magnetic moment or inducing spin-wave excitations at high current densities. Previous studies have reported spin-transfer-induced excitations in Cu/Co multilayers and nickel wires, as well as spin-transfer-driven moment reversals in manganite junctions and point contacts. In this study, the researchers use a simpler geometry – lithographically patterned pillars – to study spin-transfer effects. These pillars allow for a quantitative study of spin-transfer phenomena and testing of theoretical models. The study confirms that in low applied magnetic fields, spin-polarized electrons flowing from the thin Co layer to the thick layer can switch the moment of the thin layer antiparallel to the thick-layer moment, while a reversed current produces a switch back to the parallel orientation. However, in the pillar geometry, the spin-polarized current is incident on an isolated ferromagnetic particle, so the domain which reverses is not exchange coupled to a continuous magnetic layer. The reorientations occur at far more modest current densities than in previous studies. The researchers use the giant magnetoresistance (GMR) effect as a probe of the relative orientation of the two Co layers. They fabricate pillars with a known thickness and diameter, allowing for a quantitative study of spin-transfer phenomena. The results show that the spin-transfer effect can induce magnetization reversal at low current densities, but at higher magnetic fields, the effect is dominated by spin-wave excitations. The study also shows that the damping parameter α, which is crucial for spin-transfer theory, is consistent with experimental data. However, the effect of the external field on the critical currents required to induce switching in low H indicates a value of α more than ten times higher, suggesting that the switching is more complex than a simple uniform rotation. This suggests that α varies at the microscopic level depending on the nature of the magnetic phenomena and that spin-transfer experiments can examine such variations.This study investigates current-driven magnetization reversal and spin wave excitations in Co/Cu/Co pillars. Using pillars with diameters of ~100 nm and two Co layers of different thicknesses separated by a Cu spacer, the researchers examine the effects of spin-polarized currents flowing perpendicular to the layers. According to spin-transfer theory, spin-polarized electrons flowing from the thin to the thick Co layer can switch the magnetic moments of the layers to an antiparallel state, while a reversed current causes switching to a parallel state. When large magnetic fields are applied, the current no longer fully reverses the magnetic moment but instead stimulates spin-wave excitations. Theoretical calculations suggest that spin-polarized currents can exert a torque on the magnetic moment of a conductor, potentially flipping the magnetic moment or inducing spin-wave excitations at high current densities. Previous studies have reported spin-transfer-induced excitations in Cu/Co multilayers and nickel wires, as well as spin-transfer-driven moment reversals in manganite junctions and point contacts. In this study, the researchers use a simpler geometry – lithographically patterned pillars – to study spin-transfer effects. These pillars allow for a quantitative study of spin-transfer phenomena and testing of theoretical models. The study confirms that in low applied magnetic fields, spin-polarized electrons flowing from the thin Co layer to the thick layer can switch the moment of the thin layer antiparallel to the thick-layer moment, while a reversed current produces a switch back to the parallel orientation. However, in the pillar geometry, the spin-polarized current is incident on an isolated ferromagnetic particle, so the domain which reverses is not exchange coupled to a continuous magnetic layer. The reorientations occur at far more modest current densities than in previous studies. The researchers use the giant magnetoresistance (GMR) effect as a probe of the relative orientation of the two Co layers. They fabricate pillars with a known thickness and diameter, allowing for a quantitative study of spin-transfer phenomena. The results show that the spin-transfer effect can induce magnetization reversal at low current densities, but at higher magnetic fields, the effect is dominated by spin-wave excitations. The study also shows that the damping parameter α, which is crucial for spin-transfer theory, is consistent with experimental data. However, the effect of the external field on the critical currents required to induce switching in low H indicates a value of α more than ten times higher, suggesting that the switching is more complex than a simple uniform rotation. This suggests that α varies at the microscopic level depending on the nature of the magnetic phenomena and that spin-transfer experiments can examine such variations.