Dzyaloshinskii-Moriya interaction and nontrivial spin textures in the Janus semiconductor monolayers <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi mathvariant="normal">V</mml:mi> <mml:mi>X</mml:mi> <mml:mi>Y</mml:mi> </mml:mrow> </mml:math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>(</mml:mo> <mml:mi>X</mml:mi> <mml:mo>=</mml:mo> <mml:mi>Cl</mml:mi> <mml:mo>,</mml:mo> <mml:mo> </mml:mo> <mml:mi>Br</mml:mi> <mml:mo>,</mml:mo> <mml:mo> </mml:mo> <mml:mi mathvariant="normal">I</mml:mi> <mml:mo>;</mml:mo> <mml:mo> </mml:mo> <mml:mi>Y</mml:mi> <mml:mo>=</mml:mo> <mml:mi mathvariant="normal">S</mml:mi> <mml:mo>,</mml:mo> <mml:mo> </mml:mo> <mml:mi>Se</mml:mi> <mml:mo>,</mml:mo> <mml:mo> </mml:mo> <mml:mi>Te</mml:mi> <mml:mo>)</mml:mo> </mml:math>
R. Caglayan, A. Mogulkoc, Y. Mogulkoc, M. Modarresi, А. Н. Руденко
Abstract
We present a density functional theory based study of a two-dimensional ferromagnetic Janus $\mathrm{V}XY$ $(X=\mathrm{Cl}, \mathrm{Br}, \mathrm{I}; Y=\mathrm{S}, \mathrm{Se}, \mathrm{Te})$ structure. The dynamical and thermal stabilities of all possible $\mathrm{V}XY$ structures consisting of chalcogen and halogen atoms in the $1T$ and $2H$ phases are determined. Among them, only the $1T$ phases of the VBrS, VIS, and VISe structures are found to be stable. These structures show semiconducting properties and demonstrate spin-orbit-induced valley splittings, reaching 0.1 eV in the VISe monolayer. These structures exhibit in-plane easy axes with Curie temperatures around $\ensuremath{\sim}100\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ estimated based on the classical Monte Carlo and quantum Green's function techniques. On the other hand, the absence of inversion symmetry in Janus $\mathrm{V}XY$ compounds gives rise to the Dzyaloshinskii-Moriya interaction with the possibility of forming chiral magnetic structures. In the absence of an external magnetic field, Janus $\mathrm{V}XY$ monolayers exhibit magnetic chiral structures at 0 K, evidenced by nonzero $Q$ (topological charge) values from Monte Carlo simulations. By applying an out-of-plane magnetic field of around 0.7 T, we observe the formation of skyrmions. At 5 K, the VIS monolayer demonstrates chiral magnetic structures, while VBrS and VISe display N\'eel-type domain walls. VISe forms a skyrmion lattice at $\ensuremath{\sim}0.1\phantom{\rule{0.16em}{0ex}}\mathrm{T}$ which does not persist beyond this value. Since all the structures have an in-plane easy axis, an in-plane magnetic field of around 0.5 T at 0 K gives rise to the formation of bimerons.