Mössbauer studies of spin density wave-superconducting Fe-As systems

The recently discovered new Fe-As based spin density wave superconducting systems are shortly reviewed. Mössbauer studies of EuFe _2-xNi_xAs₂ (x=0.0 to 0.20) by ⁵⁷Fe and ¹⁵¹Eu isotopes are reported. In pure EuFe₂As ₂ the iron orders magnetically at 200 K, while the Eu orders antiferromagnetically at 18 K. The 4.2 K studies show hyperfine fields of 8.5 T and 26 T for ⁵⁷Fe and ¹⁵¹Eu respectively. Ni substitution for iron leads to a decrease in the SDW magnetic transition temperature. This phase transition is below 90 K for x>0.09. For x=0.20, the ¹⁵¹Eu studies at 4.2 K show magnetic order (hyperfine field of 28 T) while the iron displays, no magnetism but only a very small hyperfine field (1.4 T), probably transferred from the now ferromagnetic Eu sublattice.