Effect of site preference of 3d atoms on the electronic structure and half-metallicity of Heusler alloy Mn₂YAl

The site preference of 3d atoms Y in Mn₂YAl (Y = V, Fe, Co) alloys and its influence on their electronic structures and magnetism have been studied by first-principles calculations. The results prove that elements with more valence electrons than Mn tend to enter the A (0, 0, 0) and C (, , ) sites and elements with fewer electrons prefer the B (, , ) site (Wyckoff positions). Meanwhile, it is found that for Mn₂VAl and Mn₂FeAl, a high spin polarization can be obtained whether the Y atom enters the (A, C) or the B site. In particular, Mn₂VAl is half-metallic whether it forms the Cu₂MnAl type or the Hg₂CuTi type of structure. And a 100% spin polarization can be retained even when a 25% Mn-V antisite disorder occurs. This is quite preferable in practical applications. It is also found that the higher-valent element such as Co at the B (, , ) site has opposite effects and tends to close the energy gap. Finally, a systemic summarization on the electronic and magnetic properties of Mn₂YAl (Y = Ti, V, Cr, Mn, Fe and Co) alloys was made. All of them except for Mn₂TiAl are predicted as half-metals. The calculated total spin moment is an integral value and increases from -3ν_B/f.u. for Mn₂TiAl to +2ν_B/f.u. for Mn₂CoAl with increasing number of valence electrons. This agrees with the Slater-Pauling curve quite well. All the Mn₂YAl alloys studied here are ferrimagnets.