Magnetization states and switching in narrow-gapped ferromagnetic   nanorings
  We study permalloy nanorings that are lithographically fabricated with narrow gaps that break the rotational symmetry of the ring while retaining the vortex ground state, using both micromagnetic simulations and magnetic force microscopy (MFM). The vortex chirality in these structures can be readily set with an in-plane magnetic field and easily probed by MFM due to the field associated with the gap, suggesting such rings for possible applications in storage technologies. We find that the gapped ring edge characteristics (i.e., edge profile and gap shape) are critical in determining the magnetization switching field, thus elucidating an essential parameter in the controls of devices that might incorporate such structures. 
Jie Li, Sheng Zhang, Chris Grigas, Rajiv Misra, Jason Bartell, Vincent   H. Crespi, Peter Schiffer
cond-mat.mes-hall cond-mat.other