Magnetic imaging and domain nucleation in CrSBr down to the 2D limit

TL;DR

This study uses nano SQUID-on-tip microscopy to directly image magnetic properties and domain structures in CrSBr flakes from monolayer to few-layer, revealing preserved ferromagnetism, layer-dependent antiferromagnetic coupling, and stable anisotropy down to the 2D limit.

Contribution

It provides the first direct magnetic imaging of CrSBr at the monolayer level, demonstrating preserved magnetic order and domain formation in ultra-thin layers.

Findings

Ferromagnetic order persists down to monolayer CrSBr.

Antiferromagnetic coupling appears from bilayer onwards.

Néel magnetic domain walls are observed in single layers.

Abstract

Recent advancements in 2D materials have revealed the potential of van der Waals magnets, and specifically of their magnetic anisotropy that allows applications down to the 2D limit. Among these materials, CrSBr has emerged as a promising candidate, because its intriguing magnetic and electronic properties have appeal for both fundamental and applied research in spintronics or magnonics. Here, nano SQUID-on-tip (SOT) microscopy is used to obtain direct magnetic imaging of CrSBr flakes with thicknesses ranging from monolayer (N=1) to few-layer (N=5). The ferromagnetic order is preserved down to the monolayer, while the antiferromagnetic coupling of the layers starts from the bilayer case. For odd layers, at zero applied magnetic field, the stray field resulting from the uncompensated layer is directly imaged. The progressive spin reorientation along the out-of-plane direction (hard axis) is also measured with a finite applied magnetic field, allowing to evaluate the anisotropy constant, which remains stable down to the monolayer and is close to the bulk value. Finally, by selecting the applied magnetic field protocol, the formation of N\'eel magnetic domain walls is observed down to the single layer limit.