Experimental and computational study of nearly half-metallic V2CoGa

Here, we present the results of a combined computational and experimental study of electronic, magnetic, and structural properties of V2CoGa, a Heusler alloy that exhibits high spin polarization values in an ordered crystal structure. Our calculations indicate that this compound crystallizes in an inverted cubic structure. The magnetic alignment is ferrimagnetic, due to the anti-aligned magnetic moments of two vanadium sub-lattices. The calculated magnetization value for the ordered structure is 1.97 μB/f.u. at the equilibrium lattice constant of 5.898 Å. Our calculations indicate that V2CoGa in its ordered crystal structure retains high spin polarization values of around 90% under mechanical pressure. At the same time, this material exhibits a strong tendency toward A2-type atomic disorder, which has a detrimental impact on spin polarization values. In addition, the magnetization magnitude for the disordered cell is 0.38 μB/f.u. Experimentally, arc-melted samples crystallize in the predicted inverted cubic structure with A2-type disorder. To optimize the crystal structure, the samples were annealed at various temperatures. The cubic phase is preserved up to 700 °C, while annealing above this temperature leads to phase separation. X-ray diffraction patterns, analyzed using Rietveld refinement for a cubic crystal structure (space group F-43m), yields a lattice parameter of 5.929 Å, consistent with theoretical predictions. Thermomagnetic measurements reveal a magnetic transition near room temperature (295 K). Above the transition, the DC susceptibility follows Curie–Weiss behavior, with a calculated effective magnetic moment of 3.6 μB per formula unit. Given the detrimental effect of A2 disorder on spin polarization, minimizing this disorder is essential to realize the full potential of V2CoGa as a high-spin-polarization material.