Stability of magnetic configurations in nanorings
  The relative stability of the vortex, onion and ferromagnetic phases in nanorings is examined as a function of the ring geometry. Total energy calculations are carried out analytically, based on simple models for each configuration. Results are summarized by phase diagrams, which might be used as a guide to the production of rings with specific magnetic properties. 
P. Landeros, J. Escrig, D. Altbir, M. Bahiana and J. d'Albuquerque e   Castro