Theory of magnetism in the van der Waals magnet CrI3

TL;DR

This paper investigates the microscopic origins of anisotropic ferromagnetism in CrI3, highlighting the roles of Heisenberg-Kitaev-Gamma interactions, Dzyaloshinskii-Moriya interactions, and the effects of external electric fields on topological magnon properties.

Contribution

It demonstrates that both Kitaev and DMI interactions influence magnon topology in CrI3, and shows how electric fields can induce DMI, affecting spin textures.

Findings

Nearest neighbor exchange described by HKGamma model

DMI on next nearest neighbors influences magnon topology

Electric field can induce DMI, affecting spin textures

Abstract

We study the microscopical origin of anisotropic ferromagnetism in the van der Waals magnet CrI3. We conclude that the nearest neighbors exchange is well described by the Heisenberg-Kitaev-Gamma (HKGamma) model, and we also found a nonzero Dzyaloshinskii-Moriya interaction (DMI) on next nearest neighbors. Both Kitaev and DMI are known to generate a non-trivial topology of the magnons in the honeycomb lattice and have been used separately to describe the low energy regime of this material. We discuss that including one or the other leads to different signs of the Chern number. Furthermore, the topological gap at K-point seems to be mainly produced by DMI, despite it is one order of magnitude smaller than Kitaev. Finally, we show that by applying an external electric field perpendicular to the crystal plane, it is possible to induce DMI on nearest neighbors, and this could have consequences in non-collinear spin textures, such as domain walls and skyrmions.