We identify substrate steps as the origin of the pinning of magnetic domain walls in highly perfect epitaxial microislands. This explains the poor magnetic properties often shown by thin films and nanostructures.

Determining the type of defects causing pinning of magnetic domain walls is a long-lasting aim of magnetic materials engineering. This knowledge would allow first to understand the origin of the different magnetic properties of thin films and nanostructures as compared to the reference bulk materials and second, it would be of utmost importance for the tailoring of these properties, for example, towards the implementation of disruptive applications for information processing and storage in spintronics using novel concepts related to magnetic domain wall motion. In this work, we have performed a detailed correlative structural, magnetic and chemical analysis of (non-stoichiometric) epitaxial cobalt ferrite micrometric crystals by x-ray magnetic circular dichroism combined with photoemission microscopy, low-energy electron microscopy and atomic force microscopy. The magnetization vector inside the islands was resolved at the nanoscale [see Figure (b)], as obtained from magnetic images taken at different x-ray incidence angles (a). The location of the magnetic domain walls was correlated with the presence of different types of defects as revealed by the different microscopies (c). This, together with the results of micromagnetic simulations, suggests that the main source of pinning in these microcrystals are linear structural defects induced in the spinel structure by the substrate steps underneath the islands [Figure (d) depicts the magnetic domains together with different types of defects.] Our result, expected to be of general validity for oxide-based magnetic materials, represents an important contribution to the understanding of the magnetic properties of thin films and nanostructures and is relevant for applications in spintronic devices. S. Ruiz-Gómez, A. Mandziak, L. Martín-García, J.E. Prieto, P. Prieto, C. Munuera, M. Foerster, A. Quesada, L. Aballe and J. de la Figuera, "Magnetic domain wall pinning in cobalt ferrite microstructures", Applied Surface Science 600, 154045 (2022).