Structural, half-metallic and elastic properties of the half-Heusler compounds NiMnM (M = Sb, As and Si) and IrMnAs from first-principles calculations

Abstract

The structural, half-metallic and elastic properties of the half-Heusler compounds NiMnM (M = Sb, As and Si) and IrMnAs were investigated using first-principles calculations within the generalized gradient approximation (GGA) based on density function theory (DFT). The most stable lattice configurations about site occupancy are (Ni)4a(Mn)4c(Sb)4d, (Ni)4a(Mn)4c(As)4d, (Ni)4a(Mn)4c(Si)4d and (Ir)4a(Mn)4c(As)4d, respectively, and the exchange of elements in Wyckoff position 4c and 4d results in an identical (symmetry-related) phase. The half-Heusler compounds show half-metallic ferromagnetism with a half-metallic gap of 0.168 eV, 0.298 eV, 0.302 eV and 0.109 eV, respectively, and the total magnetic moments (Mtot) are 4.00 μB, 4.00 μB, 3.00 μB and 3.00 μB per formula unit, respectively, which agree well with the Slater–Pauling rule based on the relationship of valence electrons. The compound (Ir)4a(Mn)4c(As)4d with half-metallic ferromagnetic character was reported for the first time. The individual elastic constants, shear modulus, Young's moduli, ratio B/G and Poisson's ratio were also calculated. The compounds are ductile based on the ratio B/G. The Debye temperatures derived from the average sound velocity (νm) are 327 K, 332 K, 434 K and 255 K, respectively. The predicted Debye temperature for NiMnSb agrees well with the available experimental value, and the Debye temperatures for the rest three compounds were reported for the first time.