Multiscale approaches on two-dimensional magnetic materials: from atomistic to mesoscale level

Some of these materials also stabilise vortex-antivortex spin texture at low temperatures. These vortex structures are similar to those from the XY model. We find that the XXZ model can not reproduce the magnitude of the experimental Tc of CrI3 if only first-nearest neighbour interactions are included.

We thus extended the XXZ model to include more neighbour interactions as well as higher-order exchange terms and Dzyaloshinskii-Moriya interactions. This extended model gives a better estimation of the critical temperature for several materials, including the chromium trihalides family (CrX3, X=F, Cl, Br, I). Modeling the magnon spectra using this model within the linear spin-wave theory gives good agreement with the experimental results.

In particular, we show that for CrI3 the quantum effects are essential when it comes to describing the critical exponent in a Curie-Bloch law, and the shape of magnetisation versus temperature curve. We present a study of the magnetic domain in CrI3 monolayer and show that the domains are metastable. The boundary between the magnetic domains called the domain walls (DW) is in the majority of Néel type (97 %), with the rest being either Bloch type or hybrids.

Finally, we show the nucleation of topological spin texture (TST) in CrCl3. We identify these TSTs as merons and anti-merons. The TSTs are stabilised through the dipole-dipole interaction.

They are dynamic and can annihilate through non-trivial processes.