Theoretical and experimental study of half-metallic properties in V₂CoAl

Here, we present results of a combined computational and experimental study of electronic, magnetic, and structural properties of V₂CoAl, a Heusler alloy exhibiting nearly half-metallic electronic structure at equilibrium. Our calculations indicate that this alloy crystallizes in inverted Heusler cubic structure. The magnetic alignment of this material is ferrimagnetic, due to the anti-aligned magnetic moment of two vanadium sub-lattices. V₂CoAl retains its nearly 100% spin polarization under compression of the unit cell. At the same time, the spin polarization is strongly reduced under expansion of the unit cell. The reduction of the spin polarization at larger lattice parameters is due to the rigid shift of the spin-up states with respect to the Fermi level, which results in modified exchange splitting. Although the perfectly ordered cubic structure is assumed in the theoretical calculations, the bulk sample prepared using arc melting and annealing crystallizes in the disordered cubic structure. With proper annealing conditions (700 °C for 1 week), samples with B2 type disorder have been obtained. The disordered sample shows ferrimagnetic order with a Curie temperature of about 80 K, and high-field (μ₀H = 9 T) magnetization at 2K of 0.6 emu/g.