57Fe Mössbauer spectroscopic studies of single-crystalline KxFe2-yS2 and KxFe2-ySe2

We have investigated the physical properties of single-crystalline KxFe2-yS2 and KxFe2-ySe2 samples using 57Fe Mössbauer spectroscopy. The observed 57Fe Mössbauer spectra were reconstructed using a major antiferromagnetic ordered K2Fe4Se5 phase and a minor paramagnetic phase down to 5 K, despite being superconducting below 32.2 K in KxFe2-ySe2. The analysis of 57Fe Mössbauer spectrum for KxFe2-yS2 at 290 K confirms the presence of a major antiferromagnetic ordered K2Fe4S5 phase and a minor paramagnetic phase in the KxFe2-yS2 single crystal. The derived hyperfine interaction parameters of the paramagnetic phase in KxFe2-yS2 suggest that the microstructure of this phase in KxFe2-yS2 is similar to that of the superconducting phase in KxFe2-ySe2 although the KxFe2-yS2 single crystals exhibit no superconductivity down to 5 K.