We report direct evidence that magnetically charged superdomain walls form spontaneously in two dimensional square artificial spin ice nanostructures in response to external magnetic fields. These extended magnetic defects were revealed by the development of internal structure, which varies as a function of applied magnetic field, within the Bragg peaks of resonant soft x-ray magnetic scattering patterns. Magnetically charged superdomain walls extend over tens of lattice sites and do not necessarily align with the applied field. Our results illustrate a novel approach to detect hierarchical magnetic structures within spin textures.

We report evidence of spontaneous formation of a heterogeneous network of superdomains in two-dimensional square artificial spin ice nanostructures in externally applied magnetic fields. Coherent resonant soft-x-ray scattering from such textures gives rise to unique internal structure in Bragg peaks. The magnetic heterogeneity is locally disordered but has a zigzag texture at longer length scales. Our result suggests that the macroscopic magnetic texture is derived from the microscopic structure of the Dirac strings.