Structural, Electronic and Magnetic Properties of Mn2Co1-xVxZ (Z = Ga, Al) Heusler Alloys: An Insight from DFT Study

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 Fmm), L21b (L21 structure with partial disordering between Co and Mn atoms) and XA (space group F3m) 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.

FIRST-PRINCIPLES STUDIES OF X₂FeSi HEUSLER ALLOYS

“…Generally, the unit cell contains 4 structural units X2YZ. The location of atoms and their coordinates were discussed in our previous articles [10]. X2FeSi (Х= Mn, V)…”

“…Previous studies have investigated the electronic, magnetic, and structural properties of various Heusler compounds using both first-principle calculations based on DFT (Density Functional Theory) and experimental methods. These studies are cited in references [2][3][4][5][6][7][8]. Heusler alloys crystallize in two possible structures: L21 (spatial symmetry group Fm3m ) and XA (spatial symmetry group F43m ).…”

“…Interest in these compounds is not least because of the fact that the properties of complete Heusler alloys strongly depend on their structure and composition. Mn2FeX (X = Al, Si) compounds in L21, XA structures were studied by DFT + GGA methods in a number of works [9,10].…”

“…Recent works [7,14] also report that Mn2FeSi adopts a cubic inverse-heusler (XA) structure. Calculations with Density Functional Theory [9][10][11] have shown that the XA structure of Mn2FeSi is a semimetal with a total magnetic moment of 2 µB. Thus, it is assumed that Heusler compounds with transition metals can exhibit special properties, such as semimetallicity, both in the L21 structure and in the XA structure, depending on the chemical structure.…”