Abstract:
Structural, electronic, and magnetic properties of Mn2Co1-xVxZ (Z = Ga, Al, x = 0, 0.25,
0.5, 0.75, 1) Heusler alloys were theoretically investigated for the case of L21
(space group Fm3m),
L21b (L21 structure with partial disordering between Co and Mn atoms) and XA (space group F43m)
structures. It was found that the XA structure is more stable at low V concentrations, while the L21
structure is energetically favorable at high V concentrations. A transition from L21
to XA ordering
occurs near x = 0.5, which qualitatively agrees with the experimental results. Comparison of the
energies of the L21b 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 L21 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 Mn2Co1-xVxZ alloy (Z = Ga, Al) at x = 0.5 for XA ordering. In the
case of the L21 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.
