Effects of vortex chirality and shape anisotropy on magnetization reversal of Co nanorings (invited)

The effects of vortex chirality and shape anisotropy on the magnetization reversal of thin Co nanorings with and without slots have been investigated using off-axis electron holography and micromagnetic simulations. Stepped hysteresis loops were determined and typical well-defined states, including onion states, vortex states, flux-closure (FC) states, and omega (Omega) states were identified during reversal for different element shapes. The chirality of the vortex (vortices) formed after the onion states determined the switching mechanism. The Co nanorings and slotted rings with applied field parallel to the slots showed multistep switching via onion-FC-onion mode, also involving the formation and annihilation of vortex (vortices), whereas slotted rings with applied field perpendicular to the slots exhibited simple one-step switching by abrupt chirality reversal of the FC states. The influence of shape anisotropy on switching fields is also discussed in terms of demagnetization energy. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3358233]