DFT analysis of defect-induced changes in half-metallicity of the perfect structure α-CoMnSb half-Heusler for smart spintronic device applications

Half-Heusler alloys have emerged as promising candidates for smart spintronic device applications, gaining significant attention over the past decade due to their high spin polarization. Using density functional theory, we investigated the structural, electronic, and magnetic properties of the perfect structure $\alpha$-CoMnSb half-Heusler alloy, as well as the effect of defects on its half-metallicity. The computed lattice parameters closely match previously reported experimental and theoretical results. While the calculated formation energy confirms the alloy’s structural stability, the presence of anti-site defects introduces relative instability in the structure ( $\Delta H_f^{\alpha }<\Delta H_f^{\gamma }<\Delta H_f^{\beta }$ ). The calculated band structures of the perfect structure $\alpha$-CoMnSb show metallic behavior in the spin-up channel and semiconducting behavior in the spin-down channel, which supports its half-metallic nature. The density of states analysis in the spin-down channel of the perfect structure CoMnSb indicates that Mn-d states primarily contribute to the conduction band, while Co-d states dominate the valence band. The total magnetic moment of 3 ${\mu }_B$, an integer value, further confirms its half-metallic ferromagnetic behavior. The electronic properties revealed that anti-site defects reduced spin polarization in $\alpha$-CoMnSb, while vacancy defects transformed it from a half-metallic ferromagnetic to a metallic antiferromagnet.