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Zusammenfassung:
The paper presents Mossbauer spectroscopy investigation on
superconducting Rb Fe-0.8 Se-1.6 (2) exhibiting nanoscale phase
separation and two its derivatives: Cu-doped Rb Fe-0.8 Cu-1.56 Se-0.04
(2) and Fe-deficient Rb Fe-0.7 Se-1.4 (2). The spectra reveal the
presence of the same dominant magnetic sextet in the samples, which is
assigned to the Fe 16i sites of the ae5xae5x1 superstructure. This
magnetic part is independent on the modification of the sample and does
not undergo any changes after doping or deviation of stoichiometry. In
contrast, the minor non-magnetic doublet in the spectra of Rb Fe-0.8
Se-1.6 (2), which is attributed to the superconducting nanoscale phase,
is sensitive to such modifications. After doping with Cu, the relative
intensity of non-magnetic doublet significantly decreases together with
suppression of superconductivity. On the other hand, the Fe-deficient
sample is entirely magnetically ordered below 250 K including in the
minor nanoscale phase. A discussion of Mossbauer spectroscopic data and
comparison with previous studies on other Fe chalcogenide analogues
allow to conclude the nanosized phase separation is also observed in
non-stoichiometric and doped modifications of Rb Fe-0.8 Se-1.6 (2).
