First-principles study on the effect of defects on the electronic and magnetic properties of the Ti 2 NiAl inverse Heusler alloy

The effect of atomic antisite and swap defects on the electronic and magnetic properties of Ti 2 NiAl inverse Heusler alloy is investigated by the first-principles calculations within density functional theory. In the ordered Ti 2 NiAl alloy, there are eight antisites and five swaps which are established by the replacement of an atom by another and the exchange in positions of atoms, respectively. The Ni Ti(A) antisite is found to be the most probable defect due to the lowest formation energy, whereas the least probable defects are the Al Ti(A)/Ti(B) and Ni Al/Ti(B) antisites as well as Ni-Ti(A) and Al-Ti(B) swaps due to the higher formation energies compared with Ni Ti(A) antisite. The Ti Ni/Al and Al Ni antisites as well as Al-Ti(A)/Ni and Ni-Ti(B) swaps are highly unlikely to be formed due to the positive values of formation energy. Moreover, we deduce from the relative binding energy of the swap with respect to their antisites that the Ni prefers atomic antisite to site swap, while Al prefers site swap to atomic antisite. The spin polarization is markedly reduced in Ni/Al Ti(B) antisite as well as Ni-Ti(A) and Al-Ti(B) swaps due to the occurrence of defect states at the Fermi level, while a very high spin polarization is obtained for Ni/Al Ti(A) antisites and only the Ni Al antisite retains the half-metallicity with a perfect spin polarization. The magnetic moments of all the likely defected structures decrease in comparison to the ordered Ti 2 NiAl mainly due to the decrease of local magnetic moments of the defect atom and its near neighbors. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2014