Stacking tunable interlayer magnetism in bilayer CrI3

TL;DR

This paper reveals that interlayer magnetism in bilayer CrI3 can be tuned by stacking order, with different mechanisms governing intra- and inter-layer couplings, opening new avenues for magnetic property control in 2D materials.

Contribution

It identifies a new stacking order responsible for anti-ferromagnetic coupling and elucidates distinct mechanisms for intra- and inter-layer magnetic interactions in CrI3 bilayers.

Findings

Anti-ferromagnetic coupling linked to C2/m stacking order.

Distinct mechanisms: super-exchange and direct-exchange interactions.

Stacking order manipulation can tune interlayer magnetic properties.

Abstract

Diverse interlayer tunability of physical properties of two-dimensional layers mostly lies in the covalent-like quasi-bonding that is significant in electronic structures but rather weak for energetics. Such characteristics result in various stacking orders that are energetically comparable but may significantly differ in terms of electronic structures, e.g. magnetism. Inspired by several recent experiments showing interlayer anti-ferromagnetically coupled CrI3 bilayers, we carried out first-principles calculations for CrI3 bilayers. We found that the anti-ferromagnetic coupling results from a new stacking order with the C2/m space group symmetry, rather than the graphene-like one with R3 as previously believed. Moreover, we demonstrated that the intra- and inter-layer couplings in CrI3 bilayer are governed by two different mechanisms, namely ferromagnetic super-exchange and direct-exchange interactions, which are largely decoupled because of their significant difference in strength at the strong- and weak-interaction limits. This allows the much weaker interlayer magnetic coupling to be more feasibly tuned by stacking orders solely. Given the fact that interlayer magnetic properties can be altered by changing crystal structure with different stacking orders, our work opens a new paradigm for tuning interlayer magnetic properties with the freedom of stacking order in two dimensional layered materials.