Magnus Nord

The ability to rationally design materials with specific properties is a major motivator in materials science and condensed matter physics. Driven by this motivation and by the potential to open new technological avenues, researchers are continually pushing the boundaries of established materials while pioneering new ones. This push has led to newly developed techniques for fabricating, handling, and transferring freestanding oxide membranes (FOMs), providing a new avenue to overcome traditional oxide epitaxial growth limitations, which relies on specific substrates and synthesis conditions. These advances enable the design and creation of novel materials with previously inaccessible interface symmetries, stacking configurations, and atomic reconstructions, opening exciting possibilities for exploring new physics and developing innovative device architectures using atomically engineered complex oxides. At the same time, these advancements present new challenges in the synthesis, membrane transfer, characterization, and final functionalization of FOMs. The field is still in its early stages and necessitates further scientific and technological progress. This roadmap offers an overview of the current state of the field and perspectives on its future, highlighting opportunities, challenges, and guiding principles for the research community.

In low‐dimensional magnetic structures, magnetostatic energy minimization yields a uniform spin‐texture, resembling that of a macroscopic bar magnet, thereby limiting their scope for applications. Here, the formation of non‐collinear spin‐textures such as Néel‐type domain walls with perpendicular core magnetization, stable under ambient conditions, in magnetic nanostructures with dimensions reduced to ≈25 nm, is experimentally demonstrated. A single‐step magnetic writing process is deployed, wherein a nano‐focused beam of penetrating ions displaces atoms locally and converts a short‐range ordered precursor alloy that is paramagnetic to a strain‐relaxed lattice that is ferromagnetic, thus manifesting a controllable spin‐texture evolution. Simulations show that the spin‐textures rely on the presence of symmetry breaking due to crystallographic misalignments within the confined geometries. Theoretical considerations yield the critical dimension below which perpendicular Néel walls are stabilized. These results provide a direct route to implementing spatially confined non‐collinear spin‐textures generating local perpendicular magnetic fields, that are necessary in applications such as spin‐transport and spin‐based quantum sensing.

FeSn is a room-temperature antiferromagnet composed of alternating Fe3Sn kagome layers and honeycomb Sn layers. Its distinctive lattice allows the formation of linearly dispersing Dirac bands and topological flatbands in its electronic band structure, positioning FeSn as an ideal candidate for investigating the interplay between magnetism and topology. In this study, we investigate the epitaxial growth of FeSn thin films on GaAs(111) substrates by molecular beam epitaxy. A significant challenge in this growth process is the diffusion of Ga and As from the substrate into the deposited films and the diffusion of Fe into the substrate. This diffusion complicates the formation of a pure FeSn phase. Through a comprehensive analysis—including reflection high energy electron diffraction, high-resolution x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and vibrating sample magnetometry—we demonstrate that the Sn evaporation temperature plays a critical role in influencing crystallinity, surface morphology, and magnetic behavior of the films. Our results show that while it is difficult to grow a single-phase FeSn film on GaAs due to diffusion, optimizing the Sn evaporation temperature can enhance the dominance of the FeSn phase, partially overcoming these challenges.

Structural phase transitions are an important aspect of functional materials due to the strong coupling between the functional properties and crystal structure. Transmission electron microscopy (TEM) is a powerful technique used to examine materials all the way down to single atomic columns. Studying the structure of materials at temperatures from room temperature to above 1000 degrees Celsius with TEM is today routine, thanks to improvements in chip-based in-situ TEM-holders. Studying the structural changes can be done in several ways, from conventional TEM (cTEM), electron diffraction (ED) or atomic resolution STEM. Due to advances in fast pixelated electron detectors it is now possible to acquire a STEM diffraction pattern for each probe position in the scan, yielding a 4-dimensional dataset (4D-STEM). This gives highly detailed information about the crystal structure at the nanoscale, but also gives very large and complex data.