Magnetization states in coupled Ni80Fe20 bi-ring nanostructures

The effects of magnetostatic and exchange coupling between two circular Ni80Fe20 rings on the magnetization reversal process and spin configuration are investigated using focused magneto-optic Kerr measurements and magnetic force microscopy measurements. When the two rings are contiguous and exchange coupled, the reversal occurs via a three-stage process leading to a significant reduction of the vortex-onion switching fields when compared to magnetostatically coupled ring pairs or isolated rings of the same lateral dimensions. For exchange-coupled rings, the chirality of the vortices in the two rings is correlated. The experimental results are compared to micromagnetic simulations.