Effects of d-band hole doping on electronic structure, magnetism, and superconductivity in Fe- and Co-doped MgCNi3 -: art. no. 064525

Electronic structures and magnetism of the nonoxide perovskite MgCNi3-xTx compounds (x=0, 1, 2, and 3; T=Co and Fe), based on recently found superconducting MgCNi3, have been investigated with first-principles all-electron full-potential linearized augmented plane-wave calculations within the local-(spin) density approximation. From the results of total-energy calculations, it is expected that (i) the suppression of superconductivity occurs faster for the Fe-doped case than for the Co-doped case with increase of x, and (ii) ferromagnetic transitions occur when xgreater than or equal to2 for the Co-doped cases, while the Fe-doped cases become ferromagnetic before x=2. From the calculated density of states, it is found that the superconductor MgCNi3 becomes paramagnetic and then ferromagnetic, as we increase the number of minority spin d-band holes via Co and Fe doping at Ni sites. A hypothetical system, MgC(FeCoNi), has also been calculated and found to be ferromagnetic with magnetic moments of 0.97, 0.24, and 0.03 mu(B) for Fe, Co, and Ni, respectively, which are roughly proportional to the number of d-band holes of minority spin. These features are well explained by d-band spin splitting, as in conventional metallic ferromagnets.