Elongated antiferromagnetic skyrmion in two-dimensional RuF4

Two-dimensional (2D) antiferromagnetic (AFM) skyrmions are free from stray magnetic field and skyrmion Hall effect, and can be driven by a small current density up to a high speed, desirable for low-power spintronic applications. However, most 2D AFM skyrmions are realized in complex heterostructured materials, which impedes the dense integration of spintronic devices. Here, we propose that 2D AFM skyrmions can be achieved in ruthenium tetrafluoride (RuF₄) monolayer using hybrid functional theory combined with atomistic spin dynamics simulations. Our study indicates that 2D RuF₄ is dynamically stable and its nondegenerate vibration modes in optical branches are either Raman or infrared active. Furthermore, 2D RuF₄ acts as an indirect bandgap semiconductor with an out-of-plane AFM state. Notably, the presence of a weak Dzyaloshinskii-Moriya interaction in 2D RuF₄ leads to a spin spiral ground state at low temperatures, enabling the formation of AFM skyrmions with possible length modulation by an external magnetic field. Our results give insight into 2D RuF₄ and may provide an intriguing platform for 2D AFM skyrmion-based spintronic applications.