Stability, electronic band structure, magnetic, optical and thermoelectric properties of CoXCrZ (X = Fe, Mn and Z = Al, Si) and FeMnCrSb quaternary Heusler

Abstract

• The stability of these quaternary Heusler alloys has studied from the calculation of their cohesion energy. • The magnetization of these quaternary Heusler comes mainly from the 3d electrons of the Fe, Co, Mn and Cr atoms. In these materials, one spin has a finite density of states at the Fermi level, the other has a band gap. • The electronic structure of Heusler alloys depend on the degree of structural order and distribution of the atoms in the crystal lattice. CoFeCrAl, CoFeMnSi, CoMnCrSi, and FeMnCrSb Heusler alloys show SGS behavior with high Curie temperatures, thus making them suitable substitutes for diluted magnetic semi-conductors. • The increase in temperature for the spin up case reduces the figure of merit and increases the total electronic conductivity in these quaternary Heusler. • The resistivity of studied quaternary alloys is little sensitive to the temperature, while the electronic conductivity and power factor are proportional to the temperature. Ab-initio simulations based on density functional theory as contained in the WIEN2k code using GGA, GGA+U, and mBJ approximations were used to perform the calculations. The energy of cohesion is minimal for FeMnCrSb, indicating that it is the most stable structure, with a lattice constant of 5.95 Å and 6.2184 Å for GGA and GGA+U. The ferromagnetic state is less stable than ferrimagnetic states in all studied quaternary Heusler. All the band structures are metallic, with the exception of the spin up case using GGA+U and mBJ approaches, where the semiconducting character is predicted. The amount of absorption and band gap validate the candidature of CoFeCrAl, CoFeMnSi, CoMnCrSi, and FeMnCrSb as absorber materials for photovoltaic devices. The high values of 0.8, 0.9, 0.95 and 1 for figure of merit (ZT) at 300 K were obtained for CoFeMnSi, CoFeCrAl, CoMnCrSi, and FeMnCrSb allowing their use in spintronic and thermoelectric applications. The resistivity of studied quaternary alloys is little sensitive to the temperature, while the electronic conductivity and power factor are proportional to the temperature. Ferromagnetic (Ferro) and possible ferrimagnetic (Ferri) configurations of quaternary Heusler XX'YZ.