Fig. 3
Surface antiferromagnetic order of BiFeO3 films. a, b XMLD polar scans at the Fe L 3 edge of Pt(2 nm)/BiFeO3 thin film for the down state and the up state, respectively. In each scan the light polarization angle θ E varies from 0° to 90° for a fixed azimuthal angle ϕ M, where ϕ M = 0° corresponds to the incident light wave vector parallel to the substrate steps \([1\bar 10]_{{\mathrm{pc}}}\) direction. The continuous lines are best-fit results (Supplementary Note 6 and Supplementary Table 2) for the shown data points. For the down state a, fitting gives the same single-cycloid plane given by ND results within ~ 2°. For the up state b, the fitting assumes the same single-cycloid plane given by ND results with an additional surface collinear AF component with a weight of 25% (see text). Panels c, d are simulations for one of the bulk single-crystal (\(\bar 1\bar 12\)) and (112) spin-cycloid planes (inset) in down state and up state, respectively. The error bars show the precision of the measurements defined as the standard deviation from the fits
