Figure 4. Layer-dependent magnetoresistance measurements.

a, Optical and AFM images of a completed PtSe₂ device and its crystal, respectively. Dashed area represents the scanned AFM region. b. Cross-sectional plots along the red and black lines in a. AFM scans show that crystals used in device C and device D has one-layer difference (~ 0.6 nm) in their heights. c, Magnetic field dependence of ΔR measured from the device C (6.45 nm thick). d, Magnetic field dependence of ΔR measured from device D (~ 7.05 nm thick). e, AFM image of a PtSe₂ crystal having multiple one-layer thick fragments on its surface. Top inset shows the cross-sectional plots along the black line in e. Black color arrows in e and top-inset e indicate the one-layer thick fragments. Bottom-inset e shows the optical image of the corresponding device. Black solid line represents the scale bar (5 µm) f, Magnetic field dependence of ΔR measured from the device E shown in e. We would like to note that the change in device resistance in these samples has opposite sign compared to the thinner devices shown in Fig. 2-a and Fig. S4-a. Such opposite switching signs were previously observed in Co and CoFe films.³⁵ To determine the origin of this behavior, the effect of the number of layers, distribution of defects and their effect on magnetism need to be extensively investigated.