Diffracted magneto-optical Kerr effect (MOKE) technique was used to study the quasistatic magnetization switching of thin-film permalloy ring structures. Two different switching mechanisms were observed, dependent on the width of the annular portion of the ring. For small widths, a two-step switching is found, from an initial onion state to a state of circulation magnetization around the ring to a final onion state. In the wider rings, the switching from the circulation state to the onion state takes place via nucleation of a vortex within the annulus. The presence of the vortex is determined by the higher spatial frequency information revealed by diffracted MOKE, and through comparison with micromagnetic simulation.
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Saturation magnetization is ; exchange constant equals .
