The effects of various point defects and lattice distortions have been studied on the structural, electronic, and magnetic properties of the ${\mathrm{Co}}_2\mathrm{MnAl}$ alloy, considering the thermodynamically feasible range for the disorder concentrations. The ${\mathrm{Al}}_{\mathrm{Mn}}$ binary antisite-disordered structures $({\mathrm{Co}}_2{\mathrm{Mn}}_{0.9375}{\mathrm{Al}}_{1.0625} \text{and} {\mathrm{Co}}_2{\mathrm{Mn}}_{0.875}{\mathrm{Al}}_{1.125})$ and $({\mathrm{Co}}_{\mathrm{Mn}}+{\mathrm{Al}}_{\mathrm{Mn}})$-ternary antisite-disordered structure $\left({\mathrm{Co}}_{2.0625}{\mathrm{Mn}}_{0.875}{\mathrm{Al}}_{1.0625}\right)$ may be formed spontaneously during the synthesis of ${\mathrm{Co}}_2\mathrm{MnAl}$ due to their negative relative formation energies. The Al-deficient structures resulting from ${\mathrm{Co}}_{\mathrm{Al}}$ and ${\mathrm{Mn}}_{\mathrm{Al}}$ binary antisite disorder $({\mathrm{Co}}_{2.0625}{\mathrm{MnAl}}_{0.9375},$ ${\mathrm{Co}}_{2.125}{\mathrm{MnAl}}_{0.875},$ ${\mathrm{Co}}_2{\mathrm{Mn}}_{1.0625}{\mathrm{Al}}_{0.9375}, \text{and} {\mathrm{Co}}_2{\mathrm{Mn}}_{1.125}{\mathrm{Al}}_{0.875})$ and from $({\mathrm{Co}}_{\mathrm{Al}}+{\mathrm{Mn}}_{\mathrm{Al}})$-ternary antisite disorder $\left({\mathrm{Co}}_{2.0625}{\mathrm{Mn}}_{1.0625}{\mathrm{Al}}_{0.875}\right)$ exhibit perfect half-metallicity. All other antisite disorders have a marginal effect on the half-metallic properties, and the disordered ${\mathrm{Co}}_2\mathrm{MnAl}$ maintains the high spin polarization $(\ge 70\%)$ along with nearly the same magnetization as the $L{2}_1\text{-ordered}$ structure. Conversely, vacancy defects seriously affect the electronic and magnetic properties with rapid shrinking of the minority pseudogap. Also, the effect of vacancy occurrence on the structural, electronic, and magnetic properties is found to be very susceptible to their concentrations. For lattice distortions, the uniform strain $(\mathrm{\Delta }V/V_0)$ has a minimal effect on spin polarization and magnetization. Under negative strain within the range $-10\%\le \mathrm{\Delta }V/V_0\le 7\%$ (for $5.50\AA \le a\le 5.58\AA$), the strained structures showed perfect half-metallicity. For uniform strain >7%, spin polarization decreases monotonically; however, it remains high, reaching $\sim 60\%$ at $\mathrm{\Delta }V/V_0=10\%$ $(a=5.88\AA )$. Contrarily, the tetragonal distortions, except for small distortion values $(\mathrm{\Delta }c/a\le \sim \pm 0.10)$, lead to significant degradation in half-metallic behavior. Moreover, the elongation along the $c$ axis (with compression of the $ab$ plane) is found to be the favored condition for the occurrence of tetragonal distortion over compression along the $c$ axis (with elongation of the $ab$ plane). Thus, the resulting perfect half-metallicity in disordered ${\mathrm{Co}}_2\mathrm{MnAl}$ suggests that the occurrence of disorder could also be beneficial sometimes for spintronic applications.

• Received 6 January 2024
• Revised 16 February 2024
• Accepted 27 February 2024

DOI:https://doi.org/10.1103/PhysRevMaterials.8.034405