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

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Science  07 Jun 2019:
Vol. 364, Issue 6444, pp. 973-976
DOI: 10.1126/science.aav6926

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A detailed look into 2D magnetism

The van der Waals material chromium triiodide (CrI3) is a ferromagnet in the bulk but appears to become antiferromagnetic when thinned to a few atomic layers. Thiel et al. used a local magnetometry technique based on diamond nitrogen-vacancy centers to study the magnetism of these thin films at the nanoscale (see the Perspective by Fernández-Rossier). In agreement with previous results, films with odd numbers of layers had magnetization values consistent with that of a single layer, indicating antiferromagnetic coupling. But when the researchers' probe caused an accidental puncture, the magnetization of a nine-layer film increased approximately ninefold to a value expected in a ferromagnetic material. Further characterization suggested that the puncture had caused a structural transition, linking the structural and magnetic properties of this enigmatic system.

Science, this issue p. 973; see also p. 935


The discovery of ferromagnetism in two-dimensional (2D) van der Waals (vdW) crystals has generated widespread interest. Making further progress in this area requires quantitative knowledge of the magnetic properties of vdW magnets at the nanoscale. We used scanning single-spin magnetometry based on diamond nitrogen-vacancy centers to image the magnetization, localized defects, and magnetic domains of atomically thin crystals of the vdW magnet chromium(III) iodide (CrI3). We determined the magnetization of CrI3 monolayers to be ≈16 Bohr magnetons per square nanometer, with comparable values in samples with odd numbers of layers; however, the magnetization vanishes when the number of layers is even. We also found that structural modifications can induce switching between ferromagnetic and antiferromagnetic interlayer ordering. These results demonstrate the benefit of using single-spin scanning magnetometry to study the magnetism of 2D vdW magnets.

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