Study of structural, magnetic and electronic properties of a new off-stoichiometric series of full-Heusler alloy Co2Nb1+Z1− (Z = Sn, In, Ga): Ab initio approach

Using ab initio calculation, we investigate systematically the structural, electronic and magnetic properties of Co2Nb1+xZ1−x (x = 0, 0.25, 0.50). Here, Plane-Wave self-consistent field (PWscf) program implemented in open-source Quantum Espresso software package within generalized gradient approximation (GGA) - Perdew-Burke-Ernzerhof (PBE) for the exchange-correlation functional has been used. Equilibrium lattice parameters in cubic austenitic phase of Co2Nb1+xZ1−x (x = 0, 0.25, 0.50) have been inquired. It has been found out that except Co2NbSn, all the compositions do not show martensitic structural transition. The microscopic origin for this has been associated with Jahn-Teller distortion of Co 3deg orbitals in close proximity of the Fermi level. The density of states for both tetragonal and 4 O orthorhombic structure in martensitic phase of Co2NbSn have been investigated. Moreover, from the density of states plots we have recognized the metallic character of Co2NbSn. However, Co2NbGa & Co2NbIn and all of the off-stoichiometric alloys have been anticipated to possess partial half-metallic character. Furthermore, we have examined the total magnetic moment and average atomic magnetic moments in off-stoichiometric Co2Nb1+xZ1−x in the cubic phase to understand the effect of Nb doping in stoichiometric compounds. Nb doping increases the total magnetic moment due to increased Nb-Co hybridization of d orbitals.