Spin-glass behavior of semiconducting K x Fe 2 − y S 2

We report the discovery of ${\mathrm{K}}_{x}$Fe${}_{2\ensuremath{-}y}$S${}_{2}$ single crystals, isostructural to ${\mathrm{K}}_{x}$Fe${}_{2\ensuremath{-}y}$Se${}_{2}$ superconductors. The sulfide compound is a small gap semiconductor and shows spin-glass behavior below 32 K. Our results indicate that stoichiometry, defects, and the local environment of FeCh ($\text{Ch}=\text{S},\text{Se}$) tetrahedra have important effects on the physical properties of isostructural and isoelectronic ${\mathrm{K}}_{x}$Fe${}_{2\ensuremath{-}y}$Ch${}_{2}$ compounds.