High-entropy magnetism of murunskite

• DOI: 10.48550/arxiv.2406.17108
• Publication Date: 2024-06-24
• Authors: Davor Tolj; Prashant Obed Reddy; Ivica Živković; Luka Akšamović; Jian-Rui Soh; K. Komędera; I. Biało; C. M. N. Kumar; Trpimir Ivšić; Mario Novak; O. Zaharko; C. Ritter; Thomas Grange; Wojciech Tabiś; I. Batistić; L. Forró; H. M. Rønnow; D. K. Sunko; Neven Ž. Barišić
• Keywords: Magnetism

Murunskite (K$_2$FeCu$_3$S$_4$) is a bridging compound between the only two known families of high-temperature superconductors. It semiconductor like parent compounds cuprates, yet isostructural to metallic iron-pnictides. Moreover, both families, it has an antiferromagnetic (AF)-like response with ordered phase occurring below $\approx$ 100 K. Through comprehensive neutron, M\"ossbauer, and XPS measurements on single crystals, we unveil AF nearly commensurate quarter-zone wave vector. Intriguingly, identifiable magnetic atoms, iron, are randomly distributed over one-quarter available crystallographic sites in 2D planes, while remaining occupied by closed-shell copper. Notably, any interpretation terms spin-density challenging, contrast iron-pnictides where Fermi-surface nesting can occur. Our findings align disordered-alloy picture featuring interactions up second neighbors. paramagnetic state, iron ions either Fe$^{3+}$ or Fe$^{2+}$ oxidation states, associated distinct identified M\"ossbauer spectroscopy. Upon decreasing temperature appearance interactions, these signals merge completely into third, implying orbital transition. completes cascade (local) transitions that transform atoms from fully orbitally magnetically disordered homogeneously inverse space, but still real space.