Structural, electronic and magnetic properties of Ni₂XAl (X= V, Cr, Mn, Fe, and Co) Heusler alloys: An ab initio study

Nickel-based Ni₂XAl (X ​= ​V, Cr, Mn, Fe, and Co) Heusler alloys for both L2₁ and L1₀ crystal structures are studied by using the density functional theory. The magnetization energy and formation energy of Ni₂XAl Heusler alloys are calculated. We found that in the ideal L2₁ structure, ferromagnetic (FM) state is more stable than nonmagnetic (NM) and antiferromagnetic (AF) states, except Ni₂VAl. The ground state for Ni₂VAl is the nonmagnetic state. The so-called Bain paths method is applied to study the stability of Ni₂XAl alloys under tetragonal distortion. We found that Ni₂FeAl and Ni₂CoAl are possible ferromagnetic shape materials (FSMs). We also found that Ni₂CrAl and Ni₂CoAl are energetically favorable in the antiferromagnetic state in the L1₀ structure. To study the stability between L2₁ and L1₀ crystal structure, we calculate the cohesive energy for comparison. We also calculate the elastic constants, bulk modulus, shear modulus, and universal elastic anisotropy to study the mechanical stability in L2₁ and L1₀ crystal structure. The spin polarization for the L2₁ structure is calculated whilst the largest spin polarization is smaller than 80%.