Strain engineering of magnetic exchange and topological magnons in chromium trihalides from first-principles

Recent experiments evidence the direct observation of spin waves in chromium trihalides and the presence of a gap at the Dirac points of the magnon dispersion in bulk CrI${}_3$. However, the topological origin of this feature remains unclear and its emergence at the 2D limit has not yet been proven experimentally. Herein, we perform a fully self-consistent ab initio analysis to deeply understand magnetic exchange of chromium trihalides in the 2D limit. We compute the orbital dependent magnetic interactions and Curie temperatures under applied biaxial strain. Our results confirm the existence of a gap around the K high-symmetry point in the linear magnon dispersion of CrI${}_3$, which originates as a direct consequence of intralayer Dzyaloshinskii–Moriya (DM) interaction. In addition, our orbital resolved analysis reveals the microscopic mechanisms that can be exploited using strain engineering to increase the strength of the DM interaction and thus control the topological gap width in CrI${}_3$. This paves the way to the further development of this family of materials as building-blocks for topological magnonics at the limit of miniaturization.