Flower-like dynamics of coupled Skyrmions with dual resonant modes by a single-frequency microwave magnetic field

Resonant excitations of confined systems have aroused much attention because of their potential application in future microwave devices and spintronics. Under resonant excitations, the motion of topo-logical objects exhibits circular, elliptical or even stadium-like dynamics. However, more complex non-linear resonant excitations of topological objects in confined systems have seldom been reported and the associated physical mechanism remains unclear. Here, we present an observation of flower-like resonant excitations for coupled skyrmions in Co/Ru/Co nanodisks activated by a single-frequency microwave magnetic field by means of numerical simulation. We find that flower-like dynamics of coupled skyrmions is always accompanied by an excitation of an eigenfrequency near 1.15 GHz, which is strongly associated with the large non-local deformation of the topological density distribution of coupled skyrmions. These results distinguish a skyrmion from other topological objects in dynamics and will be instrumental to the manipulation of skyrmions for applications.