Compositional disorder and its influence on the structural, electronic and magnetic properties of MgC(Ni₁₋ₓCoₓ)₃ alloys using first-principles

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First-principles, density-functional based electronic structure calculations are carried out for MgC(Ni₁₋ₓCoₓ)₃ alloys over the concentration range 0≤ x≤1, using Korringa-Kohn-Rostoker coherent-potential approximation (KKR CPA) method in the atomic sphere approximation (ASA). The self-consistent calculations are used to study the changes as a function of x in the equation of state parameters, total and partial densities of states, magnetic moment and the on-site exchange interaction parameter. To study the magnetic properties as well as its volume dependence, fixed-spin moment calculations in conjunction with the phenomenological Landau theory are employed. The salient features that emerge from these calculations are (i) a concentration independent variation in the lattice parameter and bulk modulus at x 0.75 with an anomaly in the variation of the pressure derivative of bulk modulus, (ii) the fixed-spin moment based corrections to the overestimated magnetic ground state for 0.0≤ x≤0.3 alloys, making the results consistent with the experiments, and (iii) the possibility of multiple magnetic states at x 0.75, which, however, requires further improvements in the calculations.