Current-driven switching of magnetic layers

The switching of magnetic layers is studied under the action of a spin current in a ferromagnetic metal-nonmagnetic metal-ferromagnetic metal spin valve. We find that the main contribution to the switching comes from the nonequilibrium exchange interaction between the ferromagnetic layers. This interaction defines the magnetic configuration of the layers with minimum energy and establishes the threshold for a critical switching current. Depending on the direction of the critical current, the interaction changes sign and a given magnetic configuration becomes unstable. To model the time dependence of the switching process, we derive a set of coupled Landau-Lifshitz equations for the ferromagnetic layers. Higher order terms in the nonequilibrium exchange coupling allow the system to evolve to its steady-state configuration.