Probing the Structural Stability of Novel Co, Ni and Pt-based Half-metallic Half Heusler Alloys by Ab Initio Calculations

Using first principles calculations based on density functional theory, we have studied the structural, electronic, and magnetic properties of Co, Ni and Pt-based half Heusler alloys, namely, Co$BC$, Ni$BC$ and Pt$BC$ ($B$ = Cr, Mn and Fe, $C$ = Al, Si, P, S, Ga, Ge, As, Se, In, Sn, Sb and Te). In this paper, we discussed the structural stability of these alloys by systematically analyzing the formation energy calculated for different crystal symmetries, which include, the (face-centered) cubic $C1_{b}$ ($F\bar{4}$3m), orthorhombic ($Pnma$), as well as hexagonal ($P\bar{6}2m$ and $P6_{3}/mmc$) structures. We find that the ground state structure of many alloys is different from the cubic $C1_{b}$ ($F\bar{4}$3m) symmetry, although these show half-metallicity in $C1_{b}$ symmetry. We establish from our calculations that along with the alloys with $C$ elements from group IIIA, IVA and VA, alloys with group VIA elements also are electronically stable. We predict the possibility of existence of a few novel non-cubic half-metallic half Heusler alloys