Compositional disorder and its influence on the structural, electronic, and magnetic properties ofMgC(Ni1−xCox)3

Abstract

First-principles, density-functional based electronic structure calculations are carried out for MgC͑Ni 1−x Co x ͒ 3 alloys over the concentration range 0 ഛ x ഛ 1, using Korringa-Kohn-Rostoker coherentpotential approximation method in the atomic sphere approximation. 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 ͑i͒ a concentration independent variation in the lattice parameter and bulk modulus at x ϳ 0.75 with an anomaly in the variation of the pressure derivative of bulk modulus, ͑ii͒ the fixed-spin moment based corrections to the overestimated magnetic ground state for 0.0ഛ x ഛ 0.3 alloys, making the results consistent with the experiments, and ͑iii͒ the possibility of multiple magnetic states at x ϳ 0.75, which, however, requires further improvements in the calculations.

A first-principles comparison of the electronic properties of MgCyNi3and ZnCyNi3alloys

“…In general, overestimation is not so common in the LDA. Meanwhile, when one uses a similar technique for MgCNi 3 , the calculations find a slightly underestimated value which is consistent within the limitations of the density-functional theory [4,13,14]. (ii) The authors also find N(E F ) in MgCNi 3 estimated as 13.6 states/Ryd atom, while for ZnCNi 3 , under similar approximations, it was found to be 11.01 states/Ryd atom.…”

“…for n = 3, where the sign of the coefficient a 2n for n = 1 determines the nature of the magnetic ground state, i.e., a 2 > 0 refers to a paramagnetic ground state while a 2 < 0 refers to a ferromagnetic phase. We have applied the approach described above to the study of carbon vacancies in MgCNi 3 [13] and 3d transition-metal-MgCNi 3 alloys [14].…”