Antivortex domain walls observed in permalloy rings via magnetic force microscopy

Abstract

Magnetic domain walls in patterned permalloy ring elements of different widths and thicknesses have been probed by magnetic force microscopy and micromagnetic simulations. We report the experimental observation of antivortex structures in single-layer magnetic rings, previously only theoretically predicted. Furthermore, vortex-antivortex chains are observed on occasion in wider rings that prefer a circulating flux closure state. It is possible that they are pinned transient states of the relaxation path from the magnetically saturated to the circulating flux closure state. Similar tendencies are seen in micromagnetic simulations implying that vortex-antivortex pair nucleation and annihilation are fundamental parts of the said relaxation. Finally we present a phase diagram of different domain-wall configurations as a function of ring width and thickness. © 2009 The American Physical Society.