Magnetic characterization and switching of Co nano-rings in   current-perpendicular-to-plane configuration
  We fabricated Co nano-rings incorporated in the vertical pseudo-spin-valve nanopillar structures with deep submicron lateral sizes. It is shown that the current-perpendicular-to-plane giant magnetoresistance can be used to characterize a very small magnetic nano-ring effectively. Both the onion state and the flux-closure vortex state are observed. The Co nano-rings can be switched between the onion states as well as between onion and vortex states not only by the external field but also by the perpendicularly injected dc current. 
T. Yang, M. Hara, and A. Hirohata, T. Kimura and Y. Otani