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 (Li(1–x)Fe(x)OH)FeS, [(Na(1–x)Fe(x))(OH)(2)]FeS, and K(x)Fe(2–y)S(2). Upon successful intercalation of the FeS layer, the superconducting critical temperature T (c) of mackinawite is enhanced from 5 K to 8 K for the (Li(1–x)Fe(x)OH)(δ+) intercalate. Layered heterostructures of [(Na(1–x)Fe(x))(OH)(2)]FeS resemble the natural mineral tochilinite, which contains an iron square lattice interleaved with a hexagonal hydroxide lattice. Whilst heterostructured [(Na(1–x)Fe(x))(OH)(2)]FeS displays long-range magnetic ordering near 15 K, K(x)Fe(2–y)S(2) displays short range antiferromagnetism.