Superconductivity and magnetism in iron sulfides intercalated by metal hydroxides†
Inspired by naturally occurring sulfide minerals, we present a new family of iron-based superconductors. A metastable form of FeS known as the mineral mackinawite forms two-dimensional sheets that can be readily intercalated by various cationic guest species. Under hydrothermal conditions using alkali metal hydroxides, we prepare three different cation and metal hydroxide-intercalated FeS phases including (Li1−xFexOH)FeS, [(Na1−xFex)(OH)2]FeS, and KxFe2−yS2. Upon successful intercalation of the FeS layer, the superconducting critical temperature Tc of mackinawite is enhanced from 5 K to 8 K for the (Li1−xFexOH)δ+ intercalate. Layered heterostructures of [(Na1−xFex)(OH)2]FeS resemble the natural mineral tochilinite, which contains an iron square lattice interleaved with a hexagonal hydroxide lattice. Whilst heterostructured [(Na1−xFex)(OH)2]FeS displays long-range magnetic ordering near 15 K, KxFe2−yS2 displays short range antiferromagnetism.