Study on the phase stability, mechanical and half-metallic properties of half-Heusler alloys FeMnZ (Z = Si, Ge and Sn)

This study investigated the phase stability, mechanical properties, electronic band structure and magnetic properties of the half-Heusler alloys FeMnZ (Z = Si, Ge and Sn) by first-principles calculations. The most stable structure for all the alloys is ferrimagnetic Type-I structure where Fe, Mn and Z atoms occupying sites 4a (0,0,0), 4d (0.75, 0.75, 0.75) and 4c (0.25, 0.25, 0.25). Our analysis of elastic constants and mechanical stability confirms that the alloys FeMnZ (Z = Si, Ge and Sn) are all mechanically stable. The electronic band structure demonstrates FeMnSi with the equilibrium lattice constant has spin polarization of 92.28%. Upon substitution of Si with Ge and Sn, FeMnGe and FeMnSn become true half-metals with energy gaps of 0.536 eV and 0.829 eV, respectively. The p-d orbital hybridization between transition elements and main group elements plays the important role in the formation of half-metallic energy gap. Additionally, when the lattice constant of FeMnSi is tuned from equilibrium 5.33 to 5.40 & Aring;, the total magnetic moment is changes from 0.97 to 1.0 mu B/f.u., and it becomes a true half-metal. The phonon spectra of the three alloys do not exhibit imaginary frequencies, indicating their dynamic stability.