Insulating A 2 V X 3 oxides and sulfides as ferromagnetic wires

Ferromagnetic insulators are uncommon due to the prevalence of antiferromagnetic ordering in insulating materials. In this work, we investigate a family of centrosymmetric A₂BX₃ compounds whose building blocks lack inversion symmetry; each transition metal is fivefold coordinated and forms chains of edge-sharing square pyramids in one dimension, resembling wires. Using density functional theory, we explore the structural, electronic, and magnetic properties of four compounds: K₂VO₃, K₂VS₃, Rb₂VO₃, and Rb₂VS₃. All four compounds were found to be ferromagnetic insulators with magnetizations of 1 μB per formula unit. K and Rb oxides and the Rb sulfide form nonpolar Cmcm ground states, while K₂VS₃ relaxes to an antipolar Pnma phase. Total energy differences and dynamical stability preclude the formation of polar metastable states. Electronic band structure calculations predict indirect band gaps of 3.2 eV for the oxides, while the sulfides are predicted to have direct band gaps of 0.9 eV. Bader and Born effective charge analyses revealed stronger covalent bonding in the sulfides and that the K⁺ and Rb⁺ ions have no electronic or magnetic influence on the wirelike square pyramid chains. Collectively, the electronic-structure, charge-density, spin-density, and exchange-coupling results establish the microscopic mechanism by which ligand-mediated V--X--V interactions stabilize robust ferromagnetic ordering in these ferromagnetic wires. We also demonstrate the likelihood of synthesis through thermodynamic and dynamical stability analyses for this set of predicted compounds. These results establish A₂BX₃ square-pyramidal frameworks as viable platforms for designing ferromagnetic insulating materials with tunable electronic structure.