Emergent Magnetic Order in Superconducting FeS Induced by Trace Cr Doping

Area of Science:

• Condensed Matter Physics
• Materials Science
• Solid State Chemistry

Background:

• Tetragonal iron sulfide (FeS) exhibits multiband, nodal-like superconductivity (SC) with s- + d-wave pairing symmetry.
• Low-moment disordered static magnetism in FeS suggests potential coexistence of magnetic orders (MOs) with SC.
• Understanding electronic correlations and magnetic interactions is key to novel superconducting states.

Purpose of the Study:

• To investigate the effect of chromium (Cr) doping on the electronic and magnetic properties of tetragonal FeS.
• To explore the possibility of inducing and controlling the coexistence of superconductivity and magnetic order.
• To establish a phase diagram illustrating the interplay between Cr doping, magnetic transitions, and SC.

Main Methods:

• Density functional theory (DFT) calculations to predict Cr-induced electronic and magnetic changes.
• Experimental synthesis of Cr-substituted tetragonal FeS single crystals.
• Measurements of magnetic transitions and superconducting properties, including anisotropy.

Main Results:

• Cr doping induces significant d-orbital reconstruction and local magnetic moments (~2.4 µB) at doping sites.
• A clear magnetic transition and reduced SC anisotropy were experimentally observed.
• Superconductivity persists at low Cr doping levels (below 0.05), indicating SC and MO coexistence.
• Strong spin correlations between Cr dopants and the FeS host via exchange coupling were inferred.

Conclusions:

• Substitutional Cr doping is an effective method to tune the electronic configurations and modulate SC ground states in FeS.
• The continuous injection of local moments provides a controllable route to manipulate collective orders in iron-based superconductors.
• The observed coexistence of SC and MO highlights the importance of spin correlations in these materials.