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Nanoscale mechanics of antiferromagnetic domain walls in Cr2O3
Magneto-electric antiferromagnets hold promise for future spintronic devices, as they offer magnetic field hardness, high switching speeds combined with electric and magnetic control of their order parameters, owing to the magneto-electric coupling . As information and functionality is encoded in the antiferromagnetic order parameter, its manipulation, read-out and nanoscale texture are paramount for device operation, as well as interesting from a fundamental point of view. E.g. spin-textures in such materials are theorized to carry an intrinsic magnetization . Here we study a single crystal ‘textbook’ magneto-electric antiferromagnet, Cr2O3, by nanoscale imaging of its surface magnetization via magnetic stray field imaging by scanning nitrogen vacancy magnetometry . This surface magnetization is directly linked to the bulk Neel vector of Cr2O3 and thereby allows for nanoscale imaging of antiferromagnet spin textures. After confirming magneto-electric poling , local electrodes are utilized to nucleate single domain walls, which we then study on the nanometer scale. Manipulation of the domain wall is demonstrated both by local laser heating , as well as the creation of an energy landscape for the domain wall via topographic structuring . We analyze the interaction of the domain wall with topographic islands both experimentally and in simulations. This analysis yields information about the domain wall boundary conditions at topographic edges and an estimate of the full 3D-profile of the texture based on minimizing the domain walls surface energy. A Snell like refraction of the domain wall path is found, that can be represented in an analytical approximation as a ‘refractive index’ for a given island dimension as demonstrated for a range of incidence angles.
We then observe bistable domain wall paths configurations and switching between them is demonstrated and imaged experimentally. This pinning and control of the domain wall position constitutes the main ingredients for logic devices based on domain walls in magneto-electric antiferromagnets and their fundamental study.
Keywords: antiferromagnetism; Cr2O3; mesa; NV magnetometry
Curvilinear Condensed Matter: Fundamentals and Applications 717. WE-Heraeus-Seminar, 24.-26.06.2021, Bad Honnef, Germany