Theoretical Prediction of Antiferromagnetic Skyrmion Crystal in Janus Monolayer CrSi2N2As2

An antiferromagnetic skyrmion crystal (AF-SkX), a regular array of antiferromagnetic skyrmions, is a fundamental phenomenon in the field of condensed-matter physics. So far, very few proposals have been made to realize the AF-SkX, and most have been based on three-dimensional (3D) materials. Herein, using first-principles calculations and Monte Carlo simulations, we report the identification of AF-SkX in a two-dimensional lattice of the Janus monolayer CrSi₂N₂As₂. Arising from the broken inversion symmetry and strong spin–orbit coupling, a large Dzyaloshinskii–Moriya interaction is obtained in the Janus monolayer CrSi₂N₂As₂. This, combined with the geometric frustration of its triangular lattice, gives rise to the skyrmion physics and long-sought AF-SkX in the presence of an external magnetic field. More intriguingly, this system presents two different antiferromagnetic skyrmion phases, and such a phenomenon is distinct from those reported in 3D systems. Furthermore, by contacting with Sc₂CO₂, the creation and annihilation of AF-SkX in Janus monolayer CrSi₂N₂As₂ can be achieved through ferroelectricity. These findings greatly enrich the research on antiferromagnetic skyrmions.