Effect of point defects and lattice distortions on the structural, electronic, and magnetic properties of Co2MnAl Heusler alloy

The effects of various point defects and lattice distortions have been studied on the structural, electronic, and magnetic properties of the Co₂MnAl alloy, considering the thermodynamically feasible range for the disorder concentrations. The Al₌₍ binary antisite-disordered structures (Co₂Mn₀. ₉₃₇₅Al₁. ₀₆₂₅ and Co₂Mn₀. ₈₇₅Al₁. ₁₂₅) and (Co₌₍+Al₌₍) -ternary antisite-disordered structure (Co₂. ₀₆₂₅Mn₀. ₈₇₅Al₁. ₀₆₂₅) may be formed spontaneously during the synthesis of Co₂MnAl due to their negative relative formation energies. The Al-deficient structures resulting from Co₀₋ and Mn₀₋ binary antisite disorder (Co₂. ₀₆₂₅MnAl₀. ₉₃₇₅, Co₂. ₁₂₅MnAl₀. ₈₇₅, Co₂Mn₁. ₀₆₂₅Al₀. ₉₃₇₅, and Co₂Mn₁. ₁₂₅Al₀. ₈₇₅) and from (Co₀₋+Mn₀₋) -ternary antisite disorder (Co₂. ₀₆₂₅Mn₁. ₀₆₂₅Al₀. ₈₇₅) exhibit perfect half-metallicity. All other antisite disorders have a marginal effect on the half-metallic properties, and the disordered Co₂MnAl maintains the high spin polarization (70%) along with nearly the same magnetization as the L2₁-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 (/V₀) has a minimal effect on spin polarization and magnetization. Under negative strain within the range -10%/V₀7% (for 5. 500. 16em{0ex}5. 580. 16em{0ex}), the strained structures showed perfect half-metallicity. For uniform strain >7%, spin polarization decreases monotonically; however, it remains high, reaching 60% at /V₀=10% (a=5. 880. 16em{0ex}). Contrarily, the tetragonal distortions, except for small distortion values (/a0. 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 Co₂MnAl suggests that the occurrence of disorder could also be beneficial sometimes for spintronic applications.