Challenges and insights in growing epitaxial FeSn thin films on GaAs(111) substrate using molecular beam epitaxy

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.