On the propensity of magnetism in 3d transition-metal-MgCNi₃ alloys

The changes in the electronic properties of the substitutionally disordered MgC(Ni_{1-x}T_{x})_{3} (T=Fe, Co or Cu) alloys are studied using the atomic sphere formulation of the Korringa-Kohn-Rostoker coherent-potential approximation method (KKR-ASA CPA), while the effects of incipient magnetism in these alloys are studied phenomenologically using Ginzburg-Landau coefficients in conjunction with fixed-spin moment method. We find that the disordered MgC(Ni_{1-x}T_{x})_{3} alloys have a small magnetic moment localized at Fe and Co sites for low concentrations. The overestimation of the calculated magnetic moment is likely to be due to the limitations of the local-density approximation used in the present study. However, the calculated Ginzburg-Landau coefficients clearly show that the disordered MgC(Ni_{1-x}T_{x})_{3} alloys remain paramagnetic. At expanded volumes, we also find the possibility of a ferromagnetic state for MgC(Ni_{0.95}Fe_{0.05})_{3} and MgC(Ni_{0.90}Co_{0.10})_{3}.