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.

中文翻译：

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点缺陷和晶格畸变对Co2MnAlHeusler合金结构、电子和磁性能的影响

研究了各种点缺陷和晶格畸变对结构、电子和磁性能的影响${\mathrm{钴}}_2\mathrm{锰铝}$合金，考虑无序浓度的热力学可行范围。这${\mathrm{铝}}_{锰}$二元反位无序结构$（{\mathrm{钴}}_2{\mathrm{锰}}_{0.9375}{\mathrm{铝}}_{1.0625} \text{和} {\mathrm{钴}}_2{\mathrm{锰}}_{0.875}{\mathrm{铝}}_{1.125}）$和$（{\mathrm{钴}}_{锰}+{\mathrm{铝}}_{锰}）$-三元反位无序结构$（{\mathrm{钴}}_{2.0625}{\mathrm{锰}}_{0.875}{\mathrm{铝}}_{1.0625}）$可能在合成过程中自发形成${\mathrm{钴}}_2\mathrm{锰铝}$由于它们的相对形成能为负。造成的缺铝结构${\mathrm{钴}}_{铝}$和${\mathrm{锰}}_{铝}$二元反位点紊乱$（{\mathrm{钴}}_{2.0625}{\mathrm{锰铝}}_{0.9375},$ ${\mathrm{钴}}_{2.125}{\mathrm{锰铝}}_{0.875},$ ${\mathrm{钴}}_2{\mathrm{锰}}_{1.0625}{\mathrm{铝}}_{0.9375}, \text{和} {\mathrm{钴}}_2{\mathrm{锰}}_{1.125}{\mathrm{铝}}_{0.875}）$和来自$（{\mathrm{钴}}_{铝}+{\mathrm{锰}}_{铝}）$-三元反位点紊乱$（{\mathrm{钴}}_{2.0625}{\mathrm{锰}}_{1.0625}{\mathrm{铝}}_{0.875}）$表现出完美的半金属性。所有其他反位无序对半金属性质都有边际影响，并且无序${\mathrm{钴}}_2\mathrm{锰铝}$保持高自旋极化$（\ge 70\%）$以及几乎相同的磁化强度$L{2}_1\text{-订购的}$结构。相反，空位缺陷严重影响电子和磁性能，少数赝能隙迅速缩小。此外，发现空位的出现对结构、电子和磁性的影响对其浓度非常敏感。对于晶格畸变，均匀应变$（\mathrm{\Delta }V/V_0）$对自旋极化和磁化强度的影响最小。在负应变范围内$-10\%\le \mathrm{\Delta }V/V_0\le 7\%$（为了$5.50A\le A\le 5.58A$），应变结构表现出完美的半金属性。对于均匀应变 >7%，自旋极化单调减小；然而，它仍然很高，达到$～60\%$在$\mathrm{\Delta }V/V_0=10\%$ $（A=5.88A）$。相反，四方畸变，除了小畸变值$（\mathrm{\Delta }C/A\le ～\pm 0.10）$，导致半金属行为显着退化。此外，沿$C$轴（压缩$A乙$平面）被发现是沿压缩方向发生四方变形的有利条件$C$轴（随着伸长$A乙$飞机）。因此，在无序状态下产生完美的半金属性${\mathrm{钴}}_2\mathrm{锰铝}$表明无序的发生有时也可能有利于自旋电子学应用。