Magnetic vortex stability in Ni80Fe20split rings

Magnetoresistance measurements at 300 K and 1.7 K are used to quantify the vortex state magnetic field duration in a series of Ni80Fe20 ring structures with two nm-sized gaps. The measured gap sizes are from 40 nm to 510 nm. The vortex magnetic field range of stability reduces on increasing gap size but then stabilizes and is predominantly determined by extrinsic domain wall pinning defects. Virtual domain wall mediated switching with the applied magnetic field direction parallel to the gap, reduces a stochastic switching behavior in these structures, compared to a continuous ring. A comparison of experiment with the predicted switching behavior from a micro-magnetic simulation is made and the stray fields are calculated in the vortex remanent state. The reduction in the vortex field duration with increasing gap size is more gradual than that predicted by the micro-magnetic simulation up to a gap size of ∼100 nm.