2D magnetic domain wall ratchet: The limit of submicrometric holes
The study of ratchet and crossed-ratchet effects in magnetic domain wall motion through 2D arrays of asymmetric holes is extended in this article to the submicrometric limit in hole size (small size regime). Therefore, the gap has been closed between the 2D ratchets in the range of tens-of-micrometers (large size regime) and the small size regime 1D ratchets based on nanowires. The combination of Kerr microscopy, X-ray PhotoEmission Electron Microscopy and micromagnetic simulations has allowed a full magnetic characterisation of both the domain wall (DW) propagation process over the whole array and the local DW morphology and pinning at the holes. It is found that the 2D small size limit is driven by the interplay between DW elasticity and half vortex propagation along hole edges: as hole size becomes comparable to DW width, flat DW propagation modes are favoured over kinked DW propagation due to an enhancement of DW stiffness, and pinned DW segments adopt asymmetric configurations related with Néel DW chirality. Nevertheless, both ratchet and crossed-ratchet effects have been experimentally found, and we propose a new ratchet/inverted-ratchet effect in the submicrometric range driven by magnetic fields and electrical currents respectively.