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# Nanoscale magnetic field imaging for 2D materials

## Abstract

Nanoscale magnetic imaging can provide microscopic information about length scales, inhomogeneity and interactions of materials systems. As such, it is a powerful tool to probe phenomena such as superconductivity, Mott insulating states and magnetically ordered states in 2D materials, which are sensitive to the local environment. This Technical Review provides an analysis of weak magnetic field imaging techniques that are most promising for the study of 2D materials: magnetic force microscopy, scanning superconducting quantum interference device microscopy and scanning nitrogen-vacancy centre microscopy.

## Key points

• Scanning magnetic probes have developed into powerful techniques for imaging magnetization patterns, spin configurations and current distributions with high spatial resolution and high sensitivity.

• These local probes give crucial insights into length scales, inhomogeneity and interactions that are often absent from bulk measurements of transport, magnetization, susceptibility or heat capacity.

• Using these techniques to image the recently discovered correlated states hosted in 2D materials will provide crucial local information on quantum phases, including on the spatial variation of order parameters, the presence of domains and the role of defects.

• Correlated states in 2D systems are extremely sensitive to disorder and inhomogeneity. In such a fragile environment, local measurements — with sensors whose characteristic size is smaller than the length scale of the disorder — are essential for making sense of the system.

• It is important to choose the appropriate scanning magnetic probe for the physical system under investigation: the different scaling of magnetization and current contrast with probe–sample spacing and the different physical quantities that are measured by each probe make certain techniques more amenable to certain systems.

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## Acknowledgements

We thank H.-J. Hug, J. Kirtley and A. Kleibert for insightful discussions. We acknowledge the support of the Canton Aargau and the Swiss National Science Foundation under project grant 200020-178863, via the Sinergia grant Nanoskyrmionics (grant no. CRSII5-171003) and via the NCCR Quantum Science and Technology (QSIT). C.L.D. acknowledges funding by the Swiss National Science Foundation under project grant 20020-175600, by the European Commission under grant no. 820394 ASTERIQS and by the European Research Council under grant 817720 IMAGINE.

## Author information

Authors

### Contributions

All authors researched data for the article, carried out calculations and contributed substantially to discussion of the content. L.C. made the figures, with input from E.M., N.R., C.L.D. and M.P. M.P. wrote the text, with input from E.M., L.L. and C.L.D. All authors reviewed the manuscript before submission.

### Corresponding author

Correspondence to Martino Poggio.

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### Competing interests

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Nature Reviews Physics thanks Ruslan Prozorov and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Marchiori, E., Ceccarelli, L., Rossi, N. et al. Nanoscale magnetic field imaging for 2D materials. Nat Rev Phys 4, 49–60 (2022). https://doi.org/10.1038/s42254-021-00380-9

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• DOI: https://doi.org/10.1038/s42254-021-00380-9

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