(a–d) Temperature dependence of magnetization for CrI3 at various crystal thicknesses measured with H//c at 1 kOe. Insets show the first derivative of the M(T) curves. (e) Thickness-dependent T* and Tc. (f–i) Isothermal magnetization at T = 2 K for corresponding S0-S3 samples. Insets show the enlarged low field part and the derived coercive field Hc. (j) Thickness dependence of Hc.