Mechanical and thermodynamic stabilities, half-metallic and thermoelectric comparison between CoFeMnZ (Z = Si, Ge) Heuslers by DFT

The structural, electronic, thermoelectric, mechanical, and thermodynamic properties of the new quaternary Heusler compounds, CoFeMnSi and CoFeMnGe, are studied using the first-principles calculations based on density functional theory (DFT) and Boltzmann quasi-classical theory. The results of structural calculations and elastic constants and the study of phase stability diagrams show that the considered compounds in the LiMgPdSn-type cubic structure with F4¯3m\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$F\overline{4 }3m$$\end{document} space group and stoichiometry of 1:1:1:1 are stable. The study of electronic structure using a generalized gradient approximation provides that both of these Heuslers are ferromagnetic half-metals. The thermoelectric properties of these materials are investigated at different temperatures, and it is observed that the CoFeMnSi figure of merit (ZT) can be a good candidate for thermoelectric applications. The maximum figure of merit for CoFeMnSi at 100 K is around 1.0, while it reaches the maximum for CoFeMnGe at temperatures above 1000 K.