Electrical observation of asymmetric magnetization configurations in the vortex state of NiFe and Co rings

Anisotropic magnetoresistance (AMR) measurements have been used to probe the detailed reversal mechanism of 3 μm diameter, 15 nm thick NiFe and Co rings. In the vortex state, small changes in the resistance are associated with distortion or buckling in the section of the ring magnetized antiparallel to the applied field, and the resistance changes can be similar in magnitude to the domain-wall resistance. Micromagnetic simulations showed that a distorted-vortex state forms just before the vortex-onion transition, and a reversible change between the distorted-vortex state and a fully symmetric vortex state is expected during minor loop magnetic cycling. The distorted-vortex state enables the vortex chirality in a single magnetic ring to be detected using AMR measurements. (fast track communication)