Fig. 3: Stray field detection of CrSBr.

a Optical micrograph of the studied region of the CrSBr flake (scale bar is 5 μm). The black arrow shows the direction of the magnetization easy axis of the CrSBr flake. The gray dashed line highlights the edge of the 2.4 nm CrSBr layer. b Atomic-force microscope (AFM) image of the CrSBr flake. c Height profile of the CrSBr flake, measured along its width. d Electron spin resonance frequency measured at T = 10 K along the width of the CrSBr flake. The ESR signal is measured along the white dashed lines shown in Supplementary Figs. 1 and 3. e Photoluminescence (PL) measurements of the NV-diamond and CrSBr, performed at 10 K, with excitation wavelength and power of 520 nm and 10 μW, respectively. Due to the high density of the NV centers, the PL spectrum between 600 and 800 nm is dominated by the PL signal from the NV centers. f Spatial map of the PL and ESR contrast, measured at T = 70 K, corresponding to the CrSBr region shown in the AFM image in this panel (the AFM image is presented in an adaptive nonlinear color range to highlight the small steps). g AFM height profile of the 2.4 nm step in the CrSBr flake. The data is collected from 15 individual height profiles collected along the edge of the CrSBr step. The height of 2.43 ± 0.3 nm is extracted by subtraction of the mean height values at the two height levels. h Estimated stray field at the 2.4 nm CrSBr edge (solid black line) and fit (dotted red line, see Supplementary Note 3). The error bars represent the fit uncertainty of the ensemble ESR frequency (±1 s.d.).