Since the first prediction of their existence in magnetic materials, skyrmions have been intensively investigated both theoretically and experimentally. However, it remains a challenge to manipulate skyrmions and to understand their dynamics. We study nonlinear dynamics of coupled skyrmions in Co/Ru/Co nanodisks by micromagnetic simulations and show that resonant excitation can be controlled in nanoscale magnets by a dual-frequency microwave field. Two coupled resonant modes, clockwise (CW) and counterclockwise (CCW) rotation modes, are found. Polygon-like resonant excitation is observed and modulated from triangle-like to heptagon-like dynamics by a microwave field with a commensurate frequency ratio. The quasiperiodic behavior of the excitation is related to an incommensurate ratio. We also present numerical solutions of the extended Thiele's equation for skyrmions and obtain a good agreement between the solutions and the micromagnetic simulation results. This work contributes to the understanding of skyrmion dynamics and supplies a new route to manipulating skyrmions in nanoscale magnets using resonant excitation.
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