Double-Exchange Magnetic Interactions in High-Temperature Ferromagnetic Iron Chalcogenide Monolayers

Abstract

Smythite (Fe 3 S 4 ) is an iron-based chalcogenide with a lamellar structure, different from the compositionally identical mineral greigite. Owing to their natural abundance, such transition metal chalcogenides are promising materials for low-cost spintronic-based devices. Herein, we discuss the charge transfer processes and complex magnetic ordering in a two-dimensional (2D) smythite lattice. We find that Fe 2+ =Fe 3+ redox couple and complex magnetic ordering are governing factors in the charge transfer processes. A very strong ferromagnetic in-lattice coupling is also observed, which is attributed to the presence of three Fe-centres. To describe the magnetic behaviour molecular and periodic approaches have been considered. We found a substantial increase in Curie temperature with applied mechanical stress due to opening of the double exchange interaction angle. We also observe an in-plane Jahn−Teller distortion, which is further confirmed by the spin−orbit counter plot. Our study thus provides an insight into the double exchange mechanism favoured by the Fe 2+ =Fe 3+ redox couple and results in a strong ferromagnetic ordering. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim