# Probing magnetism in 2D materials at the nanoscale with single spin microscopy

## TL;DR

This paper uses single-spin scanning magnetometry to quantitatively analyze magnetic properties of atomically thin CrI₃ crystals, revealing layer-dependent magnetization and structural effects on magnetic ordering at the nanoscale.

## Contribution

It demonstrates the application of nanoscale, quantitative magnetic imaging in 2D magnets, uncovering layer-dependent magnetization and structural influences on magnetic states.

## Key findings

- Magnetization of CrI₃ monolayers is approximately 16 μ_B/nm².
- Magnetization vanishes in even-layer CrI₃ samples.
- Structural modifications can switch between ferro- and anti-ferromagnetic states.

## Abstract

The recent discovery of ferromagnetism in 2D van der Waals (vdw) crystals has generated widespread interest, owing to their potential for fundamental and applied research. Advancing the understanding and applications of vdw magnets requires methods to quantitatively probe their magnetic properties on the nanoscale. Here, we report the study of atomically thin crystals of the vdw magnet CrI$_3$ down to individual monolayers using scanning single-spin magnetometry, and demonstrate quantitative, nanoscale imaging of magnetisation, localised defects and magnetic domains. We determine the magnetisation of CrI$_3$ monolayers to be $\approx16~\mu_B/$nm$^2$ and find comparable values in samples with odd numbers of layers, whereas the magnetisation vanishes when the number of layers is even. We also establish that this inscrutable even-odd effect is intimately connected to the material structure, and that structural modifications can induce switching between ferro- and anti-ferromagnetic interlayer ordering. Besides revealing new aspects of magnetism in atomically thin CrI$_3$ crystals, these results demonstrate the power of single-spin scanning magnetometry for the study of magnetism in 2D vdw magnets.