6533b857fe1ef96bd12b4275

RESEARCH PRODUCT

Phase separation in superconducting and antiferromagneticRb0.8Fe1.6Se2probed by Mössbauer spectroscopy

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description

${}^{57}$Fe-M\"ossbauer studies of superconducting Rb${}_{0.8}$Fe${}_{1.6}$Se${}_{2.0}$ with ${T}_{C}$ $=$ 32.4 K were performed on single-crystalline and polycrystalline samples in the temperature range 4.2--295 K. They reveal the presence of 88% magnetic and 12% nonmagnetic Fe${}^{2+}$ species with the same polarization dependence of their hyperfine spectra. The magnetic species are attributed to the 16$i$ sites of the $\sqrt{5}\ifmmode\times\else\texttimes\fi{}\sqrt{5}\ifmmode\times\else\texttimes\fi{}1$ superstructure and the nonmagnetic Fe species to a nanosized phase observed in recent structural studies of superconducting K${}_{x}$Fe${}_{2\ensuremath{-}}$${}_{y}$Se${}_{2}$ systems rather than to the vacant 4$d$ sites in the $\sqrt{5}\ifmmode\times\else\texttimes\fi{}\sqrt{5}\ifmmode\times\else\texttimes\fi{}1$ superstructure. The ${}^{57}$Fe spectrum of a single-crystalline sample in an external field of 50 kOe applied parallel to the crystallographic $c$ axis confirms the antiferromagnetic order between the fourfold ferromagnetic Fe(16$i$) supermoments and the absence of a magnetic moment at the Fe sites in the minority phase. A discussion of all spectral information and comparison with superconducting FeSe provides convincing evidence that the nanoscale phase separation is monitored by M\"ossbauer spectroscopy in Rb${}_{0.8}$Fe${}_{1.6}$Se${}_{2.0}$.