Figure 2

Figure 2: The figure shows a simplified version of the Fermi surfaces for both materials. In SrFe2As2 the experimentally observed magnetic order, which is characterized by an ordering vector Q=(π,0) can be explained as due to a spin-density-wave instability arising from the nesting of the hole (blue) and electron pockets (red) by the same vector. However, for Fe1+xTe no such Fermi-surface nesting is possible at the corresponding ordering vector Q=(π/2,π/2).