Effect of Co doping on the electronic structure of MgCNi3

Self-consistent full-potential linear muffin-tin orbital band structure calculations of the antiperovskites MgCNi3, MgCNi2Co, and MgCNiCo2 are presented. It is found that the electronic structure of MgCNi3 near the Fermi level is dominated by a Ni 3d-derived density of states peak just below the Fermi level, which provides the superconducting properties of this compound. The Co doping of MgCNi3 is accompanied by a reduction of the density of states at the Fermi level, which seems to be responsible for the reduced superconductivity in the MgCNi1-xCox system. No magnetic solution is found for MgCNi2Co and MgCNiCo2. This indicates that the hole doping does not produce the magnetic instability which can be responsible for pair breaking. The validity of the band structure calculations is confirmed by x-ray emission (C Kalpha, Ni L-2,L-3, and Co L-2,L-3) and x-ray photoelectron spectra measurements of superconducting MgC1.45Ni3 (T-c=7.5 K) and nonsuperconducting MgC1.45Ni1.5Co1.5.