The defect-induced changes of the electronic and magnetic properties in the inverse Heusler alloy Ti2CoAl

• The swap, antisite, and vacancy defects are studied in half-metallic Ti2CoAl.
• The CoTi(A) antisite is the most probable among the studied defects.
• The antisite defects almost retain the half-metallicity.
• Most of swap and vacancy defects have degraded the half-metallicity.
• High spin polarizations are detected in Co–Al swap and Ti(A) vacancy defects.

The first-principles calculations are performed to investigate the effect of swap, antisite and vacancy defects of three classes on the electronic and magnetic properties in the inverse Heusler alloy Ti2CoAl of half-metallicity. Our calculations reveal that Ti(A/B)–Co and Co–Al swaps, Ti(A/B) and Al vacancy defects as well as CoTi(A)/Al and AlTi(A)/Ti(B) antisite defects are likely to form in a concentration as high as 12.5%. Among them, CoTi(A) antisite is detected to be the most probable defect. It is shown that the spin polarizations of Ti2CoAl are considerably reduced by the Ti(A/B)–Co swap and Ti(B)/Al vacancy defects, while a quite high spin polarization around 95% is observed in Co–Al swap as well as Ti(A) vacancy. Remarkably, all the likely antisite defects almost retain the half-metallic character in a concentration of 12.5% even if they have the possibility to form. However, induced by antisites, the Fermi levels shift to the edge of band gap with small peaks arising just above the Fermi level, which may destroy the half-metallicity by spin-flip excitation.

The spin polarization and formation energy of various possible defects in inverse Heusler alloy Ti2CoAl. The triangle, star and square represent the swap, antisite and vacancy defects, respectively.Figure optionsDownload as PowerPoint slide