Frustration-induced magnetic bimerons in transition metal halide CoX2 (X = Cl, Br) monolayers

With the field of two-dimensional (2D) magnetic materials expanding rapidly, noncollinear topological magnetic textures in 2D materials are attracting growing interest recently. As the in-plane counterpart of magnetic skyrmions, magnetic bimerons have the same topological advantages, but are rarely observed in experiments. Employing first-principles calculations and Monte Carlo simulations, we predict that the centrosymmetric transition metal halide CoX2 (X = Cl, Br) monolayers can be promising candidates for observing the frustration-induced bimerons. These bimerons crystallize into stable triangular lattice under an appropriate magnetic field. Compared to the skyrmions driven by the Dzyaloshinskii-Moriya interaction or the long-ranged magnetic dipole-dipole interactions, these frustration-induced bimerons have much smaller size and flexible tunability. Furthermore, the biaxial strain provides an effective method to tune the frustration and thereby to tune the bimeron lattice. In detail, for CoCl2 monolayer, tensile strain can be applied to generate bimeron lattice, further shrink bimeron size and increase the density of bimerons. For CoBr2 monolayer with inherent bimeron lattice state, a unique orientation rotation of bimeron lattice controlled by compressive strain is predicted.