Vortex dynamics in an equilateral triangular arrangement of three magnetic disks

Magnetic vortices in micron-sized ferromagnetic disks have been of great interest because of their potential applications in data storage. While the motion of a vortex in a single isolated magnetic disk has been studied extensively, vortex dynamics in multiple-disk planar geometries remains to be fully understood. We report direct time-resolved imaging and theoretical calculations of the vortex states in an equilateral triangular arrangement of three magnetic disks with varied center-to-center spacings. The free-motion trajectories of the vortex cores in the triangular arrangement of three permalloy disks of 2 micron radius were traced using time-resolved x-ray photoemission electron microscopy at beamline 4-ID-C of the Advanced Photon Source. The temporal resolution is 90 ps. The oscillation amplitude in the tri-disks with 4.5 micron center spacing was smaller than that with 5 micron center spacing. No significant frequency shift was observed. Theoretical calculation showed both frequency shift and trajectory change due to dipolar interaction of the disks at varied spacings.