Facet tomography of chromia's magnetoelectric multipole

Artikel i vetenskaplig tidskrift, 2026

Roughness-insensitive surface magnetization is an intrinsic property of magnetoelectric antiferromagnets and is today understood as a manifestation of bulk magnetoelectric multipoles. Here, we provide an experimental quantification of the crystal-facet-dependent surface magnetization in the archetypical magnetoelectric antiferromagnet Cr2O3 and show that the data are consistent with a quadrupolar component of the bulk magnetoelectric multipolization. Using quantitative nanoscale magnetometry on lithographically defined rectangular mesas that expose 30 distinct crystallographic facets, we quantify mesa stray magnetic fields, which arise from differences between the mesa top and side-facet magnetizations. The resulting dataset supports a linear map from surface normal to surface magnetization, from which we directly infer the bulk quadrupolar component within the multipolization framework. Our work provides systematic, facet-resolved evidence of roughness-insensitive surface magnetization, including in-plane components, and delivers a quantitative route to constraining bulk multipoles from surface stray-field data. Beyond addressing the modern theory of magnetoelectric multipolization, our approach offers a generally applicable method to quantify surface magnetizations in antiferromagnetic compounds and informs the choice of crystal cuts for future spintronics devices.