Magnetostatic interactions in mesoscopic Ni80Fe20 ring arrays

We investigate, directly using magnetic force microscopy, the effect of magnetostatic interactions in arrays of Ni80Fe20 mesoscopic rings. The rings were fabricated on silicon substrate using deep ultraviolet lithography at 248 nm exposure wavelength. We observed that the transitions from onion-to-vortex and vortex-to-reverse onion magnetic states are strongly dependent on the edge-to-edge-spacing of the rings due to dipolar magnetostatic interaction. For a closely packed ring array, the transition from onion to vortex state occurs at a much lower field due to collective magnetic switching as compared with widely spaced rings. The remanent magnetic state is found to be very sensitive to the orientation of the applied field due to shape anisotropy.