Spin interactions and topological magnonics in chromium trihalide CrClBrI

TL;DR

This paper models a chromium trihalide monolayer revealing its potential for hosting topological magnon states, skyrmions, and chiral spin textures, with implications for magnonic devices and thermal Hall effects.

Contribution

It introduces a symmetry-based model for CrClBrI monolayer showing unique anisotropic interactions and topological magnon phenomena not present in single-halide counterparts.

Findings

Presence of chiral spin states like skyrmions and spin cycloids.

Magnon bands with non-zero Chern numbers and edge states.

Temperature and magnetic field-dependent magnon thermal Hall conductivity.

Abstract

The discovery of spontaneous magnetism in van der Waal (vdW) magnetic monolayers has opened up an unprecedented platform for investigating magnetism in purely two-dimensional systems. Recently, it has been shown that the magnetic properties of vdW magnets can be easily tuned by adjusting the relative composition of halides. Motivated by these experimental advances, here we derive a model for a trihalide CrClBrI monolayer from symmetry principles and we find that, in contrast to its single-halide counterparts, it can display highly anisotropic nearest- and next-to-nearest neighbor Dzyaloshinskii-Moriya and Heisenberg interactions. Depending on the parameters, the DM interactions are responsible for the formation of exotic chiral spin states, such as skyrmions and spin cycloids, as shown by our Monte Carlo simulations. Focusing on a ground state with a two-sublattice unit cell, we find spin-wave bands with nonvanishing Chern numbers. The resulting magnon edge states yield a magnon thermal Hall conductivity that changes sign as function of temperature and magnetic field, suggesting chromium trihalides as a candidate for testing topological magnon transport in two-dimensional noncollinear spin systems.