Correlated vortex chiralities in interacting permalloy dot patterns

Magnetostatic interactions in different polycrystalline permalloy dot patterns for dots with diameter 900nm and thickness 30nm are investigated through magnetic force microscopy imaging, magneto-optic Kerr effect measurements, and micromagnetic simulations. Magnetization reversal occurs through vortex nucleation∕annihilation. Vortex nucleation and annihilation fields for different interacting arrays were observed to vary with pattern type and with the applied field direction and were shown to follow the prediction of a simple point-dipole model. The vortex chirality was established by imaging vortices in a small applied field. The vortex chirality distribution was determined for different arrays and a well-defined ordering phenomenon of the vortex chirality was observed in two-dot and zigzag-dot chain patterns as well as in a honeycomb array of dots. Micromagnetic simulations well account for the type of vortex chirality ordering observed and attribute it to magnetostatic interactions that induce correlated C-state magnetization configurations among nearest neighbor dots prior to vortex nucleation.