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Abstract:
This article reviews recent experimental investigations on two binary Fe-chalcogenides: FeSe and Fe1+yTe. The main focus is on synthesis, single crystal growth, chemical composition, as well as on the effect of excess iron on structural, magnetic, and transport properties of these materials. The structurally simplest Fe-based superconductor Fe1+xSe with a critical temperature Tc approximate to 8.5K undergoes a tetragonal to orthorhombic phase transition at a temperature Ts approximate to 87K. No long-range magnetic order is observed down to the lowest measured temperature in Fe1+xSe. On the other hand, isostructural Fe1+yTe displays a complex interplay of magnetic and structural phase transitions in dependence on the tuning parameter such as excess amount of Fe or pressure, but it becomes a superconductor only when Te is substituted by a sufficient amount of Se. We summarize experimental evidence for different competing interactions and discuss related open questions. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
