Topological magnetic states are promising for ultradense memory and logic devices. Recent progress in two-dimensional magnets encourages the idea to realize topological states, such as skyrmions and merons, in freestanding monolayers. However, monolayers such as ${\mathrm{CrI}}_3$ lack Dzyaloshinskii-Moriya interactions (DMIs) and thus do not naturally exhibit skyrmions/merons but rather a ferromagnetic state. Here we propose the fabrication of $\mathrm{Cr}{(\mathrm{I},X)}_3$ Janus monolayers, in which the Cr atoms are covalently bonded to the underlying I ions and top-layer Br or Cl atoms. By performing first-principles calculations and Monte Carlo simulations, we identify strong enough DMIs, which leads to not only helical cycloid phases, but also to topologically nontrivial states, such as the intrinsic domain wall skyrmions in $\mathrm{Cr}{(\mathrm{I},\mathrm{Br})}_3$ and the magnetic-field-induced bimerons in $\mathrm{Cr}{(\mathrm{I},\mathrm{Cl})}_3$. Microscopic origins of such spin textures are revealed as well.

• Received 25 July 2019
• Revised 18 September 2019
• Accepted 28 January 2020

DOI:https://doi.org/10.1103/PhysRevB.101.060404