Strain-tunable topological antiferromagnetism of two-dimensional magnets with negative Poisson ratio

Two-dimensional materials with a negative Poisson ratio, which exhibit unique mechanical behavior that expands laterally when stretched, have attracted considerable attention for their practical applications in sensors, biomedicine, and other fields. Here, using the elastic solid theory and first-principles calculations, we screen out a series of two-dimensional (2D) auxetic magnets ${MX}_{2}$ protected by $P\overline{4}m2$ crystal symmetry. We show that various types of chiral antiferromagnetic spin configurations can be achieved. Specifically, the elliptical antiferromagnetic antiskyrmion can be stabilized in $\mathrm{Mn}{\mathrm{I}}_{2}$ and $\mathrm{Co}{\mathrm{Cl}}_{2}$ monolayers under the external strain along the $x$-direction due to the coexistence of a negative Poisson ratio and anisotropic Dzyaloshinskii-Moriya interaction. Our work thus enriches the family of 2D auxetic magnets by introducing intrinsic long-range magnetic order, and it provides a platform for investigating strain-tunable topological antiferromagnetism.