Variation of magnetization reversal in pseudo-spin-valve elliptical rings

We studied nanoscale elliptical ring shaped NiFe/Cu/NiFe trilayer pseudo-spin-valve structures. The magnetization reversal processes showed simultaneous-reversal single-step transition or double-step transition involving flux closure states. For various aspect ratios (short axis to long axis) and linewidths, transition between single-step and double-step magnetization reversals was measured to form a phase diagram. When the linewidth was reduced, edge roughness became important. Simulations of the magnetization reversal behavior agreed qualitatively with our results.