Electronic structures and magnetism of the nonoxide perovskite ${\mathrm{MgCNi}}_{3-x}{T}_x$ compounds $(x=0\mathrm{}$, 1, 2, and 3; $T=\mathrm{Co}$ and Fe), based on recently found superconducting ${\mathrm{MgCNi}}_3,$ 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 $x>~2$ for the Co-doped cases, while the Fe-doped cases become ferromagnetic before $x=2.\mathrm{}$ From the calculated density of states, it is found that the superconductor ${\mathrm{MgCNi}}_3$ 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 $0.03\hspace{0.5em}{\mu }_B$ 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.

• Received 9 August 2001

DOI:https://doi.org/10.1103/PhysRevB.65.064525