Quenched Slonczewski-Windmill in Spin-Torque Vortex-Oscillators

We present a combined analytical and numerical study on double-vortex spin-torque nano-oscillators and describe a mechanism that suppresses the windmill modes. The magnetization dynamics is dominated by the gyrotropic precession of the vortex in one of the ferromagnetic layers. In the other layer the vortex gyration is strongly damped. The dominating layer for the magnetization dynamics is determined by the current polarity. Measurements on Fe/Ag/Fe nano-pillars support these findings. The results open up a new perspective for building high quality-factor spin-torque oscillators operating at selectable, well-separated frequency bands.