Nanoscale studies of antiferromagnetic spin-textures

Magneto-electric antiferromagnets hold promise for future spintronic devices, as they offer magnetic field hardness, high switching speeds and both electric and magnetic control of their order parameters, owing to the magneto-electric coupling [1]. As information and functionality is encoded in the antiferromagnetic order parameter, its manipulation, read-out and nanoscale textures are paramount for device operation, as well as interesting from a fundamental point of view. For applications the surface plays a key-role as the interface often dictates the read/write functionalities and gains importance as thin film devices are targeted. Using scanning nitrogen vacancy magnetometry [2] we study a ‘textbook’, single crystal magneto-electric antiferromagnet Cr 2O3 and perform nanoscale imaging of its surface magnetization, which is directly linked to its magnetic order parameter. We first confirm magneto-electric poling [3] of a homogeneous antiferromagnetic order and study the stray field polarity at the surface depending on the used field configuration. Our results are consistent with a theoretically predicted topmost disordered layer [4]. In the next step local electrodes are utilized to nucleate individual single domain walls. Manipulation of the domain wall path is demonstrated both by local laser heating, as well as the creation of an energy landscape for the domain wall position via topographic structuring [2]. Analysing the domain wall path yields further information about the boundary conditions for the order parameter 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. The demonstrated 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. Understanding the intrinsic properties and stability of the magnetic order at the direct surfaces may aid in exploring their functionality in spintronic devices that often rely on spin-scattering mechanisms at the interface.