Spin waves excited by dc currents injected into single ferromagnetic thin films

It is well known theoretically and experimentally that spin waves can be excited by current in magnetic trilayer and multilayer structures where the current is spin polarized by one of the magnetizations and interacts with the others. However, it has also been observed experimentally that a nonpolarized dc current flowing through a point contact into a single ferromagnetic thin film can induce spin waves. We investigate this phenomenon using a model in which the spins of the conduction electrons interact with a nonuniform magnetization and the current is treated perturbatively. To a first-order approximation, the spin-wave modes excited by the injected current have been characterized and the relationship between the dynamic properties of the spin waves and the applied current and applied magnetic field has been established. Calculated results are then used for comparison with the experimental observations.