Structure and property correlations in FeS

Abstract

For iron-sulfide (FeS), we investigate the correlation between the structural details, including its dimensionality and composition, with its magnetic and superconducting properties. We compare, theoretically and experimentally, the two-dimensional (2D) layered tetragonal ("t-FeS") phase with the 3D hexagonal ("h-FeS") phase. X-ray diffraction reveals iron-deficient chemical compositions of t-Fe 0.93(1) S and h-Fe 0.84(1) S that show no low-temperature structural transitions. First-principles calculations reveal a high sensitivity of the 2D structure to the electronic and magnetic properties, predicting marginal antiferromagnetic instability for our compound (sulfur height of z S = 0.252) with an ordering energy of about 11 meV/Fe, while the 3D phase is magnetically stable. Experimentally, h-Fe 0.84 S orders magnetically well above room temperature, while t-Fe 0.93 S shows coexistence of antiferromagnetism at T N = 116 and filamentary superconductivity below T c = 4 K. Low temperature neutron diffraction data reveals antiferromagnetic commensurate ordering with wave vector k m = (0.25,0.25,0) and 0.46(2) μ B /Fe. Additionally, neutron scattering measurements were used to find the particle size and iron vacancy arrangement of t-FeS and h-FeS. The structure of iron sulfide has a delicate relationship with the superconducting transition; while our sample with a =3.6772(7) Å is a filamentary superconductor coexisting with an antiferromagnetic phase, previously reported samples with a > 3.68 Å are bulk superconductors with no magnetism, and those with a ≈ 3.674 Å show magnetic properties.

Robustness of superconductivity to competing magnetic phases in tetragonal FeS

“…This is markedly different to the behaviour observed in our sample, and suggests that the magnetic properties of t-FeS are strongly sample-dependent, a conclusion which is supported by Ref. 17.…”

Atomic Layer Deposition of Two-Dimensional Layered Materials: Processes, Growth Mechanisms, and Characteristics

“…FeS can be tetragonal or hexagonal phase, while NiS has a layered structure. 134 NiS also has two polymorphs, i.e., hexagonal (a-NiS) and rhombohedral (b-NiS) structures. 135 The former is metallic with a 3D structure, and the latter is insulating with a 2D millerite structure.…”

Nanocrystalline Iron Monosulfides Near Stoichiometry

“…For stoichiometric FeS, the two crystal phases that have received the most attention are troilite and mackinawite. Troilite is predicted to exhibit large room temperature magnetoelectricity, while mackinawite is reported to be an unconventional iron-based superconductor, analogous to FeSe 6 – 9 . Understanding the boundaries between and properties of compositions in this phase space is critical not only for accessing such applications but for advancing the means by which we can explore and assess complicated, defect-intolerant materials.…”

“…Whether or not these compounds form structures that are thermodynamically separable and stable or that are instead kinetically isolated from one another remains an open question. Slight changes to the Fe-S composition ratios of these materials lead to large variations in structural, chemical, optoelectronic, and other physical properties 6 , 10 , 16 , 19 , 20 . Iron defects in these materials, even at a concentration of a few percent, affect their properties in poorly understood ways 21 – 23 .…”