A semi-skyrmions-based oscillator in elliptical nanopillars with perpendicular anisotropy.

• The semi-skyrmions-based oscillation mode with GHz frequencies is observed. • The mode frequencies strongly depend on the in-plane dimension. • The mode frequency is affected by the material parameters. • The shape of the ellipse influences the velocity of the semiskyrmion. Magnetic skyrmions have been proved to be applicable to spin torque nano-oscillator. In this paper, we show dynamics of magnetic skyrmions in elliptical spin-valve nanopillar with perpendicular magnetic anisotropy (PMA) free layer and spin polarizer by using micromagnetic simulation. A novel semi-skyrmions-based oscillation mode with GHz frequencies appears in this geometry. We find that the mode frequencies strongly depend on the in-plane dimension of the elliptical nanopillar. The fitting function between the mode frequency and the perimeter of the ellipse is obtained. Simulation results also show that the exchange constant and the temperature effect have great influence on the mode frequency. [ABSTRACT FROM AUTHOR]