  The compound EuFe(2-x)Co(x)As2 was investigated by means of the 57Fe and
151Eu Moessbauer spectroscopy versus temperature (4.2 - 300 K) for x=0
(parent), x=0.34 - 0.39 (superconductor) and x=0.58 (overdoped). It was found
that spin density wave (SDW) is suppressed by Co-substitution, however it
survives in the region of superconductivity, but iron spectra exhibit some
non-magnetic component in the superconducting region. Europium orders
anti-ferromagnetically regardless of the Co concentration with the spin
re-orientation from the a-axis in the parent compound toward c-axis with the
increasing replacement of iron by cobalt. The re-orientation takes place close
to the a-c plane. Some trivalent europium appears in EuFe(2-x)Co(x)As2 versus
substitution due to the chemical pressure induced by Co-atoms and it
experiences some transferred hyperfine field from Eu2+. Iron experiences some
transferred field due to the europium ordering for substituted samples in the
SDW and non-magnetic state both, while the transferred field is undetectable in
the parent compound. Superconductivity coexists with the 4f-europium magnetic
order within the same volume. It seems that superconductivity has some
filamentary character in EuFe(2-x)Co(x)As2 and it is confined to the
non-magnetic component seen by the iron Moessbauer spectroscopy.
