LAUSR

Odd- and even-layer variations in magnetization occur in two-dimensional chromium triiodide The discovery of ferromagnetic order in monolayers of two different materials, CrI3 (1) and Cr2Ge2Te6 (2), has added ferromagnetism to the electronic properties displayed by two-dimensional (2D) crystals. Characterization of magnetic 2D crystals has relied on magneto-optical methods (1, 3) such as the Kerr effect or magnetic circular dichroism that can interrogate small sample volumes. However, these probes do not provide an absolute measurement of the magnetic moment density and have very limited spatial resolution. On page 973 of this issue, Thiel et al. (4) use sensors based on nitrogen vacancy (NV)–center scanning magnetometry (5) to map the absolute magnetic moments of 2D crystals of CrI3 with a resolution of a few tens of nanometers and show how the anomalous interlayer spin interactions vary with number of layers.