  Iron-based superconductors Ba0.7Rb0.3Fe2As2 and CaFe1.92Co0.08As2 of the
'122' family have been investigated by means of the 14.41-keV Moessbauer
transition in 57Fe versus temperature ranging from the room temperature till
4.2 K. A comparison is made with the previously investigated parent compounds
BaFe2As2 and CaFe2As2. It has been found that Moessbauer spectra of these
superconductors are composed of the magnetically split component due to
development of spin density wave (SDW) and non-magnetic component surviving
even at lowest temperatures. The latter component is responsible for
superconductivity. Hence, the superconductivity occurs in the part of the
sample despite the sample is single phase. This phenomenon is caused by the
slight variation of the dopant concentration across the sample (crystal).
