  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.
