Fig. 2: Experimental demonstration of 2D-Ferromagnetism of the Fe-DCA network on Au(111).

a XAS (displaced vertically for clarity) and corresponding (b) XMCD spectra acquired with circularly right (I⁺) and left (I⁻) polarized X-ray light for normal (0°) and grazing (70°) incidence at the L_2,3 edges of Fe. The Fe L_2,3 XAS sits on top of the Au EXAFS background. A strong out-of-plane magnetic anisotropy is evidenced by inspection. c Angular dependence of the orbital (red), effective spin (blue) and total (black) magnetic moments obtained from the sum rules. The lines follow a cosine relation: \({\mu }_{\kappa }^{\varphi=0}\cdot\cos (\varphi )\) with κ = L, S_eff, and Total. d Hysteresis loops (open symbols) obtained at the L₃ edge of Fe at normal (φ = 0°, blue) and grazing (φ = 70°, red) incidence. The solid symbols are the result of applying the sum rules to the XAS and XMCD spectra obtained at remanence after conveniently cycling the field from ±6 T to zero for both incidence angles. e Integrated area (normalized to the saturation value) of the L₃ XMCD main peak measured in normal incidence under low fields (H = 0.1 T) as a function of temperature from T = 5 K up to 60 K. The original XMCD data are shown in the inset. The Onsager 2D Ising analytical solution (dashed line) and a Monte Carlo simulation (red line), both for a honeycomb lattice are shown, satisfactorily describing the experimental data for J ≈ 2 meV. The experiment was performed crossing T_C heating up and then cooling down, exhibiting reversibility. Indeed, such T_C reversibility was reproduced on a second Au(111) substrate under H = 0.05 T (cf. Supplementary Fig. S6). f Modified Arrott-Noakes plot of isotherms with β = 0.30 and γ = 1.51 corresponding to a long-range 2D-Ising model⁴⁴.