Emergence of a noncollinear magnetic state in twisted bilayer CrI3

TL;DR

This paper reports the discovery of a noncollinear magnetic ground state in twisted bilayer CrI3, arising from competing interlayer interactions, which can be controlled by gating, opening avenues for moiré magnetism and magnetic memory devices.

Contribution

It demonstrates the emergence of a noncollinear magnetic state in twisted bilayer CrI3 due to stacking-dependent interactions, a novel finding in moiré magnetism.

Findings

Noncollinear magnetic state exists in small-twist-angle bilayer CrI3.

Transition from noncollinear to collinear FM occurs above ~3° twist angle.

Gating can control the noncollinear magnetic state via doping.

Abstract

The emergence of two-dimensional (2D) magnetic crystals and moir\'e engineering has opened the door for devising new magnetic ground states via competing interactions in moir\'e superlattices. Although a suite of interesting phenomena, including multi-flavor magnetic states, noncollinear magnetic states, moir\'e magnon bands and magnon networks, has been predicted, nontrivial magnetic ground states in twisted bilayer magnetic crystals have yet to be realized. Here, by utilizing the stacking-dependent interlayer exchange interactions in CrI3, we demonstrate in small-twist-angle bilayer CrI3 a noncollinear magnetic ground state. It consists of both antiferromagnetic (AF) and ferromagnetic (FM) domains and is a result of the competing interlayer AF coupling in the monoclinic stacking regions of the moir\'e superlattice and the energy cost for forming AF-FM domain walls. Above the critical twist angle of ~ 3{\deg}, the noncollinear state transitions abruptly to a collinear FM ground state. We further show that the noncollinear magnetic state can be controlled by gating through the doping-dependent interlayer AF interaction. Our results demonstrate the possibility of engineering moir\'e magnetism in twisted bilayer magnetic crystals, as well as gate-voltage-controllable high-density magnetic memory storage.