Superconductivity and magnetism in K-doped EuFe2As2

Superconductivity is found in 50% K-doped EuFe₂As₂ samples below 33 K. Our results from electrical resistivity, magnetic susceptibility and ⁵⁷Fe and ¹⁵¹Eu Mössbauer spectroscopy provide clear evidence that the ordering of the Fe moments observed at 190 K in undoped EuFe₂As₂ is completely suppressed in our 50% K-doped sample; thus there is no coexistence of the Fe magnetic order and the superconducting state. However, short range ordering of the Eu moments coexists with the superconducting state below 15 K. A bump in the susceptibility well below T_c as well as the broadening of the Fe Mössbauer line below 27 K evidence an interplay between the Eu magnetism and the superconducting state.