Comprehensive analysis of bulk and (001) surface properties of the quaternary Heusler compound CoTiFeGe

The study investigates the CoTiFeGe quaternary Heusler alloy, focusing on its bulk structure with various ordering types and its (001) surface terminations of ∗CoFe and ∗TiGe. Employing density functional theory (DFT), researchers analyzed the material's properties. Calculations of elastic constants provided insights into the alloy's mechanical properties. Electronic structure analysis, specifically the density of states and band structure for XA-type ordering, revealed half-metallic characteristics. Using both GGA and mBJ-GGA methods, the study found band gaps of 0.490 eV and 0.982 eV, respectively, confirming the alloy's half-metallic nature. Surface analysis showed that the ∗CoFe-terminated (001) surface loses its half-metallic ferromagnetic character, while the ∗TiGe-terminated surface maintains complete spin polarization. This finding has significant implications for potential spintronic applications. Optical property investigations of both bulk and (001) surfaces supported the material's semiconducting nature. The primary optical reflections were observed in the visible and infrared regions, with minimal loss in the same spectral range. The presence of absorption in the (001) surface suggests potential applications in optoelectronics. Additionally, the research explored the alloy's thermoelectric properties by examining its transport coefficients.