Aligned Alternating Head-to-Head and Tail-to-Tail Domain Walls in Ferromagnetic Concentric Rings

We demonstrate the concept of multi-bits storage in concentric ferromagnetic rings fabricated using electron beam lithography and lift-off technique. At remenance, we observed that no two head-to-head or tail-to-tail domain walls exist at the same location in neighboring rings. Instead, they pin themselves with that of the opposite kind of the neighboring embedded ring, thereby minimizing the total free energy of the system. A unique arrangement of aligned alternating head-to-head and tail-to-tail domain walls in rings favoring antiparallel alignment of magnetization is observed at remenance. This results in the chirality of vortex configuration in each ring to be strongly dependent on its width and magnetostatic interaction with the neighboring embedded rings. The results are in good agreement with micromagnetic simulations.