Structural, thermo-elastic, electro-magnetic and thermoelectric attributes of quaternary CoNbMnX (X = Al, Si) Heusler alloys

This investigation consists of performing the structural, thermodynamic, electronic, magnetic and thermoelectric characteristics of the quaternary Heusler CoNbMnX (X = Al, Si) alloys using DFT within Wien2k code. Our calculations show that the atomic arrangement of the two alloys CoNbMnAl and CoNbMnSi is Type-I. From the elastic constant and the formation energy values, these compounds are predicted to be mechanically and thermodynamically stable, thus can be formed experimentally. The calculated values of their bulk modulus and cohesive energy values show that CoNbMnSi is more rigid than CoNbMnAl. From the analysis of the electronic properties, CoNbMnAl is identified to be paramagnetic and semiconductor alloy with 0.15 eV narrow indirect (Γ-X) band gap. Whereas, CoNbMnSi is characterized as a ferromagnetic alloy with half-metallicity character having a total magnetic moment of 1μB. The charge density contours and Fermi surface, predict a combined covalent and ionic bond between the atoms of CoNbMnX alloys. The calculated thermoelectric parameters assume that these alloys tend to behave as p-type with the same thermoelectric efficiency for either charge carriers; hole or electron. Depending on the high Seebeck coefficient value and ZT = 1 of the present alloys, potential applications are predicted, such as spin injection materials and spintronic applications.