Theoretical Investigations of Properties of New Half-Heusler Compounds NiFeZ (Z = Si, Ge)

The half-Heusler alloys NiFeZ (Z = Si, Ge) are investigated theoretically in the general framework of Density Functional Theory (DFT). We have calculated structural, mechanical, elastic, electronic, magnetic, and optical properties using WIEN2k simulation package. To incorporate the electronic exchange-correlation energy we have used the GGA+U approximation. Both the compounds are found structurally stable, however, elastic properties show that NiFeSi is ductile while NiFeGe is brittle. Electronically, the compounds are found to be half-metals with small band gaps in the spin-down channels whereas spin-up channels are conducting. The total magnetic moments for both the compounds are ≈ 2μ_B. Optical properties including dielectric function, refractive index, extinction coefficient, reflectivity, conductivity, and absorption coefficient are also calculated and analyzed.