Symmetry breaking in the formation of magnetic vortex states in a permalloy nanodisk.

The magnetic vortex in nanopatterned elements is currently attracting enormous interest. A priori, one would assume that the formation of magnetic vortex states should exhibit a perfect symmetry, because the magnetic vortex has four degenerate states. Here we show the first direct observation of an asymmetric phenomenon in the formation process of vortex states in a permalloy nanodisk using high-resolution full-field magnetic transmission soft X-ray microscopy. Micromagnetic simulations confirm that the intrinsic Dzyaloshinskii-Moriya interaction, which arises from the spin-orbit coupling due to the lack of inversion symmetry near the disk surface, as well as surface-related extrinsic factors, is decisive for the asymmetric formation of vortex states.