Extended Data Figure 5: The sample-end experimental set-up of Sagnac MOKE.

a, For the temperature-dependent Kerr image study of 2–5-layer samples under a 0.075-T field, the specimen is loaded on a stage surrounded by a cylindrical permanent magnet and the effective magnetic field perpendicular to the specimen surface is approximately 0.075 T, measured by a Gauss meter. A quarter wave plate is placed on the quartz window. Therefore, the raw signal includes a sample Kerr rotation signal and a background signal, primarily from the Faraday effect of the quartz window. The background signal can readily be obtained by data acquisition on the bare SiO₂ substrate. A description of the remaining part of the optical set-up connecting to the polarization maintaining fibre can be found in ref. 22. b, For the study of magnetic field control of transition temperatures, a slightly modified experimental set-up is used. The cylindrical magnet in a provides a magnetic field of only very limited strength. To compare the contrasting fields, we machined the heights of copper stages to accommodate the heights of different disk magnets with contrasting field strengths: 0.065 T and 0.3 T. c, For the hysteresis study, we made a superconducting coil to accommodate the chamber. Owing to the connection between the superconducting coil and the sample stage in our set-up, the superconducting coil cannot be used for temperature-dependent studies. WD, working distance.