  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.
