Evidence of Noncollinear Spin Texture in Magnetic Moir\'e Superlattices

TL;DR

This study provides direct evidence of noncollinear spin textures in twisted bilayer chromium triiodide, revealing moiré-induced magnetic frustrations and novel magnetic phenomena in 2D moiré superlattices.

Contribution

It demonstrates the existence of noncollinear spin textures and net magnetization in twisted CrI3, driven by moiré exchange coupling, a novel magnetic behavior not seen in natural 2D magnets.

Findings

Noncollinear spins observed in twisted CrI3.

Net magnetization despite antiferromagnetic layers.

Twist angle dependence of magnetic features.

Abstract

Moir\'e magnetism, parallel with moir\'e electronics that has led to novel correlated and topological electronic states, emerges as a new venue to design and control exotic magnetic phases in twisted magnetic two-dimensional(2D) crystals. Here, we report direct evidence of noncollinear spin texture in 2D twisted double bilayer (tDB) magnet chromium triiodide (CrI$_3$). Using magneto-optical spectroscopy in tDB CrI$_3$, we revealed the presence of a net magnetization, unexpected from the composing antiferromagnetic bilayers with compensated magnetizations, and the emergence of noncollinear spins, originated from the moir\'e exchange coupling-induced spin frustrations. Exploring the twist angle dependence, we demonstrated that both features are present in tDB CrI$_3$ with twist angles from 0.5$^o$ to 5$^o$, but are most prominent in the 1.1$^o$ tDB CrI$_3$. Focusing on the temperature dependence of the 1.1$^o$ tDB CrI$_3$, we resolved the dramatic suppression in the net magnetization onset temperature and the significant softening of noncollinear spins, as a result of the moir\'e induced frustration. Our results demonstrate the power of moir\'e superlattices in introducing novel magnetic phenomena that are absent in natural 2D magnets.