Structural, Electronic and Magnetic Properties of Mn(2)Co(1-x)V(x)Z (Z = Ga, Al) Heusler Alloys: An Insight from DFT Study

Structural, electronic, and magnetic properties of Mn(2)Co(1-x)V(x)Z (Z = Ga, Al, x = 0, 0.25, 0.5, 0.75, 1) Heusler alloys were theoretically investigated for the case of L2(1) (space group Fm3 over bar m), L2(1b) (L2(1) structure with partial disordering between Co and Mn atoms) and XA (space group F4 over bar 3m) structures. It was found that the XA structure is more stable at low V concentrations, while the L2(1) structure is energetically favorable at high V concentrations. A transition from L2(1) to XA ordering occurs near x = 0.5, which qualitatively agrees with the experimental results. Comparison of the energies of the L2(1b) and XA structures leads to the fact that the phase transition between these structures occurs at x = 0.25, which is in excellent agreement with the experimental data. The lattice parameters linearly change as x grows. For the L2(1) structure, a slight decrease in the lattice constant a was observed, while for the XA structure, an increase in a was found. The experimentally observed nonlinear behavior of the lattice parameters with a change in the V content is most likely a manifestation of the presence of a mixture of phases. Almost complete compensation of the magnetic moment was achieved for the Mn(2)Co(1-x)V(x)Z alloy (Z = Ga, Al) at x = 0.5 for XA ordering. In the case of the L2(1) ordering, it is necessary to consider a partial disorder of atoms in the Mn and Co sublattices in order to achieve compensation of the magnetic moment.