Magnetostatic coupling in arrays of elongated Ni80Fe20 rings

We describe the effects of magnetostatic interactions and film thickness on the switching properties and reversal mechanisms of periodic arrays of elongated Ni80Fe20 thin film rings. The magnetization reversal process, the switching field distributions and the transition fields between different equilibrium states are strongly affected by the inter-ring spacing. For closely packed ring arrays, sharp transitions were observed from the onion-to-vortex state due to collective magnetization reversal of the rings. In agreement with micromagnetic simulations, the range of stability of the vortex state is smaller for closely packed ring arrays compared with isolated rings of similar lateral dimensions.