A team of scientists at the U.S. Department of Energy’s (DOE) Argonne National Laboratory, Northwestern University, the University of Edinburgh, the Donostia International Physics Center and the University of Arkansas has revealed how magnetic domains behave inside 2D van der Waals magnets based on Fe3GeTe2 (FGT), providing a roadmap for tuning skyrmions using material thickness and magnetic‑field conditions.
The researchers worked with a thin, layered FGT flake whose thickness changed gradually across the sample, creating regions that behave differently magnetically while still being part of the same crystal. Because FGT in this study is magnetic only at low temperature, the flake was cooled with liquid nitrogen to cryogenic temperatures while an out‑of‑plane magnetic field was applied (field cooling), setting up well‑defined initial domain patterns.
The team then used in situ cryogenic Lorentz transmission electron microscopy (cryo‑LTEM) at Argonne’s Center for Nanoscale Materials to directly watch how tiny magnetic regions nucleate, grow, move and disappear as the external field is swept through magnetization reversal. By imaging several thickness regions at once and taking advantage of natural atomic step edges formed during exfoliation, they could clearly see how thickness alone changes the domain behavior, without introducing damage from more aggressive fabrication methods. These step edges act as strong pinning sites, meaning domain walls and skyrmions tend to get “caught” there, so their motion and transformations depend strongly on the local step structure.
As the field was varied, the FGT flake exhibited a sequence of distinct magnetic patterns, including stripe‑like domains, isolated skyrmions and a faceted, patch‑like state built from 360° domain walls. The team also identified a new phase: a polygonal patch network that appears under reversed magnetic fields after particular field‑cooling conditions, showing that domain topology is very sensitive both to thickness and to the magnetic field used during cooling. In thinner regions, the balance of energies in the material favors smaller, denser skyrmions, while thicker parts support wider stripes and extended patch networks of 360° walls.
To understand why these patterns emerge, collaborators used micromagnetic simulations that reproduced the main domain phases and their evolution, confirming that sample thickness, magnetic anisotropy and applied field together control the energy landscape and thus the domain configurations. The combined imaging and simulation work shows how skyrmion size, density and transitions between domain states can be efficiently tuned by adjusting these parameters. “The overarching goal is to learn how to precisely control skyrmions so they can potentially be used in advanced, high‑density information technologies,” said Jennifer Garland, a Northwestern University visiting graduate student at Argonne and a lead author of the study, emphasizing how controlling magnetism in atomically thin FGT could enable future ultra‑dense, low‑power spintronic devices.