title: Symmetry breaking in the formation of magnetic vortex states in a permalloy nanodisk.
abstract: 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.
authors.affiliation: Center for X-ray Optics, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA. mim@lbl.gov
authors.forename: Mi-Young
authors.initials: MY
authors.lastname: Im
authors.forename: Peter
authors.initials: P
authors.lastname: Fischer
authors.forename: Keisuke
authors.initials: K
authors.lastname: Yamada
authors.forename: Tomonori
authors.initials: T
authors.lastname: Sato
authors.forename: Shinya
authors.initials: S
authors.lastname: Kasai
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Nakatani
authors.forename: Teruo
authors.initials: T
authors.lastname: Ono