Room Temperature Topological Spin Textures in 2D Janus Chromium Chalcohalides with Dual Ligand Enhanced Ferromagnetism

Strong Dzyaloshinskii–Moriya interaction (DMI) and topological spin textures in two-dimensional (2D) magnetic materials hold great potential for novel spin-based information storage and processing. The current research efforts on topological magnetism are highly limited by insufficient magnetic strength, resulting in a narrow temperature-external magnetic field (T-B) phase diagram window. In this study, 2D Janus Cr₂X₃Y₃ (X = Cl, Br, I; Y = S, Se, Te) monolayers are investigated by employing first-principles calculations and atomic spin simulations, demonstrating desirable characteristics such as high Curie temperatures, significant DMI, and chiral spin textures benefited from the ligand substitution. Notably, stable field-free room-temperature magnetic skyrmions are observed in the Cr₂Br₃S₃ monolayer and can persist under long-range magnetic and temperature fields. Additionally, meron chains and skyrmion chains are preserved in the Cr₂I₃S₃ monolayer under appropriate magnetic field and temperature. Based on the tight-binding approximation, a ligand-resolved six-electron model is developed to distinguish superexchange interactions through X- and Y-ligand hopping channels. This model elucidates the interplay between electronegativity and orbital degeneracy, shedding light on their influence on magnetic strength. This discovery highlights and expands the potential of ligand substitution for achieving high-temperature topological magnetism in 2D magnetic materials.