Effect of spatially asymmetric dipolar interactions in the magnetization reversal of closely spaced ferromagnetic nanoisland arrays

The magnetization reversal process of interacting elongated nanoislands is presented here. The magnetization reversal has been investigated by means of magneto-optical Kerr effect magnetometry, analyzing the beams reflected and diffracted by the array, magnetic force microscopy, and micromagnetic simulations. The nanoislands have an aspect ratio of 4.2 and are arranged in chiral square units forming a checkerboard array. Due to this particular arrangement, each island is subjected to a spatially asymmetric dipolar interaction field. We found that for certain directions of the applied field this specific character of the dipolar interaction affects the reversal process profoundly. In these cases the magnetization reversal takes places via the nucleation and displacement of a vortex state in two of the four nanoislands in every square unit, at variance with single domain rotation process generally observed for other directions of the applied field.