Automotive domain wall propagation in ferromagnetic rings

Automotive domain wall propagation is a self-propelling motion utilizing the energy stored in a particular energy reservoir of the spin structure to speed up domain wall beyond its equilibrium value given by external driving force and damping. Such a concept of DW motion is of great interest due to recent development of spintronic devices based on domain walls, where automotion could be used to assist or prevent domain wall pinning at low driving fields^1-2. In turn, most of studies so far have been devoted to the automotion invoked by DW transformations from metastable to stable states^3-4; appearing at sufficiently high magnetic fields strong and enough to trigger domain wall spin structure transformations associated with motion. While several theoretical studies predict the presence of DW automotion at zero magnetic fields in straight wires⁵, it is not clear whether the reduction of Zeeman energy can be strong enough to overcame pinning (and move walls) in circular ferromagnetic rings, where stray fields emanating from semi-closed flux are much smaller as compared to straight geometry.