Probing the physical properties of iron-rich olivine Fe2GeS4 and Fe2GeSe4 compounds: DFT calculations

The structural, electronic, and magnetic characteristics of olivine-type materials, particularly Fe2GeSe4 and Fe2GeS4, were investigated using the Full-Potential Linearized Augmented Plane Wave (FP-LAPW) method within the Wien2k code, employing Density Functional Theory (DFT). Various approaches, including GGA, GGA + U, and TB-mBJ, were were applied to manage the exchange–correlation potential in calculations. Fe2GeSe4 showed metallic properties under the GGA, while the GGA + U method revealed half-metallic ferromagnetism (HMF) properties. In contrast, Fe2GeS4 displayed stable ferromagnetic (FM) and semiconductor properties across all three methods (GGA, GGA + U, and TB-mBJ). Analysis of the total and partial density of states highlighted hybridization types, particularly exchange interactions between Selenium and Sulfur p orbitals and Iron d orbitals. This interaction promoted ferromagnetic coupling in Fe ₂GeSe ₄, while Fe ₂GeS ₄ exhibited primarily ferromagnetic tendencies. Mechanically these compounds are stable, brittle, anisotropic, and hard to scratch. Our compounds are brittle due to their Pugh’s ratio of less than 1.75. The covalent bonding of the structure revealed by the Poisson ratio is less than 0.25 for the two compounds. These findings suggest Fe ₂GeSe ₄ and Fe ₂GeS ₄ are promising for spintronic applications and high performance electronic devices.