2D magnetic domain wall ratchet: the limit of submicrometric holes

Abstract

In the last decade, magnetic ratchet effect of domain walls has been proposed by several groups as a working principle for spintronic devices like magnetic diodes or shift registers. Indeed, some of the proposed strategies are promising candidates to be seen in the near future in working devices. As an alternative route, we have succeeded in producing and observing magnetic ratchet effects, as well as crossed-ratchet effects, in a ferromagnetic thin film where we have nanopatterned 2D arrays of asymmetric holes in the submicrometric limit for hole sizes. The combination of Kerr microscopy, X-Ray PhotoEmission Electron Microscopy and micromagnetic simulations has allowed a full magnetic characterisation of the domain wall (DW) propagation processes over the whole array and the local DW morphology and pinning at the holes. It is found that the DW dynamics in the submicrometric size limit are governed 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 Nèel DW chirality. 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.