Magnetism and stability of all primitive stacking patterns in bilayer chromium trihalides

TL;DR

This study systematically explores all possible stacking arrangements in bilayer chromium trihalides, revealing their stability and magnetic properties, and providing insights consistent with experimental observations and potential for novel configurations.

Contribution

It introduces a comprehensive enumeration and stability ranking of all primitive stacking patterns in CrX3 bilayers, including novel configurations with no bulk counterpart.

Findings

All observed bulk stacking configurations are recovered.

Stacking sequences with opposite chirality are identified.

A correlation between stacking and magnetic ordering is established.

Abstract

Chromium trihalides, CrX$_3$ (with X = Cl, Br, I), are a family of layered magnetic materials that can be easily exfoliated to provide ferromagnetic monolayers. When two layers are stacked together to form a bilayer the interlayer exchange coupling can be either ferromagnetic or antiferromagnetic depending on the stacking sequence. Here we combine crystallographic arguments based on the close-packing condition with first-principles simulations to enumerate all possible stacking patterns in CrX$_3$ bilayers that preserve the spatial periodicity of each layer. We recover all configurations observed in bulk crystals and disclose stacking sequences with no bulk counterpart where the two layers have opposite chirality. Stacking sequences are ranked according to their relative stability and a preferential interlayer magnetic ordering is assigned to each of them. Simulations provide a consistent picture to frame all current experimental observations on bulk and exfoliated CrX$_3$ crystals, with interesting implications for future measurements, including synthetic bilayers with non-standard stacking patterns.