Superconductivity and magnetism in Iron Sulfides Intercalated by Metal Hydroxides

TL;DR

This study introduces new iron sulfide-based superconductors intercalated with metal hydroxides, demonstrating enhanced superconductivity and magnetic properties, and explores their structural and magnetic characteristics.

Contribution

The paper reports the synthesis of new intercalated FeS phases with enhanced superconductivity and magnetic ordering, expanding the family of iron-based superconductors with novel layered structures.

Findings

Superconducting $T_c$ increased from 5 K to 8 K upon intercalation.

Layered heterostructures exhibit long-range magnetic order near 15 K.

Different intercalates show distinct magnetic behaviors, including antiferromagnetism.

Abstract

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)$^{\delta+}$ 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.