Vortex Formation During Magnetization Reversal of Co Slotted Nanorings

Electron holography can provide direct visualization and quantitative information about magnetization configurations, which is essential for determination of reversal mechanisms. The remanent states and switching behavior of Co slotted nanorings have been investigated using off-axis electron holography and Lorentz microscopy. The 30-nm-thick Co elements, with outer and inner diameters of 450 and 150 nm, and slot angle of 60deg, were lithographically patterned into 3 times 3 arrays. Depending on whether the external field was applied parallel or perpendicular to the slot direction, the individual elements exhibited onion or flux-closure configurations at remanence, with three-step or one-step hysteresis behavior, respectively. Vortex formation was observed during the three-step magnetization reversal, whereas abrupt reversal in the chirality of flux closure states was evident for the one-step hysteresis loop.