Coexistence of magnetism and superconductivity in 112-type iron pnictides EuFeAs2 doped with Co

Polycrystalline samples of Eu(Fe1−xCox)As2 with x = 0.05, 0.10 and 0.13 were systematically studied by the 57Fe Mössbauer spectroscopy as well as with magnetization and electrical resistivity measurements. The obtained results deliver interesting information about the interplay of magnetism and superconductivity in the studied compounds at low temperatures. As it was shown, all three compounds exhibit the Eu2+ related long-range antiferromagnetic order below 40 K and the superconductivity in FeAs layers which emerges deep in the antiferromagnetic phase. In the case of Eu(Fe0.95Co0.05)As2, the 57Fe Mössbauer spectroscopy data gives clear evidence that this system undergoes the SDW transition at 80 K thus the superconductivity observed below 18 K coexists with SDW and 4f-europium magnetic order within the same volume. In the samples with higher Co doping, the SDW order is fully suppressed and the superconductivity occurs at a much higher critical temperature close to 28 K.