Magnetic and structural transitions in layered iron arsenide systems: AFe₂As₂ versus RFeAsO

Resistivity, specific-heat, and magnetic-susceptibility measurements performed on SrFe₂As₂ samples evidence a behavior very similar to that observed in LaFeAsO and BaFe₂As₂, with the difference being that the formation of the spin-density wave and the lattice deformation occur in a pronounced first-order transition at T₀=205 K. Comparing further data evidences that the Fe magnetism is stronger in SrFe₂As₂ and in EuFe₂As₂ than in the other layered FeAs systems investigated up to now. Full potential local-density approximation band-structure calculations confirm the large similarity between the compounds, especially for the relevant low energy Fe 3d states. The relation between structural details and magnetic order is analyzed.