Magnetization reversal induced by irregular shape nanodots in square arrays

Ni₈₀Fe₂₀ nanodots in square arrays of irregular shape (C_1h(m) and x-, y-translations symmetry) and circular shape (D_4h (4/mmm)) nanodots of the same area were fabricated under controlled exposure conditions by e-beam lithography, ion beam sputtering coating and further lift-off. The center-to-center nearest dot distances was 700 nm in all the measured arrays. An unpatterned film was fabricated in the same IBS batch for comparison purposes. Structures and magnetic properties were characterized using AFM, SEM and high-sensitivity focused magneto-optical Kerr effect (MOKE). The mechanism of the magnetization reversal of arrays is discussed in two different scenarios: vortex and single-domain. It has been shown that circular dots reverse only through vortex configuration whereas the irregular does either via single-domain and vortex configuration, depending of the dot size. Variable domain phases are confirmed by OOMMF (Object Oriented Micromagnetic Framework) micromagnetic simulations.