Nanowire spin-torque oscillator with non-uniform polarizer: a micromagnetic study

This paper studies the dynamical response of a ferromagnetic nanowire driven by a localized spin-polarized current for in-plane and out of plane field. At zero field and with a shifted vortex polarizer, we found in the dispersion relationship a finite wave vector also for microwave current frequency approaching the ferromagnetic resonance frequency. We have interpreted this result by assuming that a given mixed mode of the wire having a frequency close to the quasi-uniform mode is excited by the spin-current. For out-of plane cases, we observed that the wave vector related to the excitation of a propagating spin-wave at certain frequency does not depends on the kind on how it is generated, i.e. dc or microwave current.