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

The effects of disorder and incipient magnetism in MgC(Ni1-xTx)3 (T≡Fe, Co or Cu) alloys are studied using coherent-potential approximation and Ginzburg-Landau coefficients. The first-principles, local-density-functional-based calculations for substitutionally disordered Fe and Co impurities in the Ni sub-lattice of MgCNi3, in low concentrations, show that incipient magnetism resides in these materials. The overestimation of the calculated magnetic properties points to the limitations of the local-density approximation. However, using a phenomenological approach based on Ginzburg-Landau coefficients and the fixed-spin moment method, we show that MgC(Ni1-xTx)3 alloys remain paramagnetic. At expanded volumes, we also find the possibility of a ferromagnetic state for MgC(Ni0.95Fe0.05)3 and MgC(Ni0.90Co0.10)3 alloys.