A study was made of the electronic structure of 3-dimensional transition-metal–MgB2 alloys, Mg0.97TM0.03B2, (TM = Sc, Ti, V, Cr Mn, Fe, Co, Ni, Cu, Zn) using the Korringa–Kohn–Rostoker coherent-potential approximation method in the atomic-sphere approximation. For unpolarized calculations, the results for Mg0.97TM0.03B2 alloys were similar to that of 3d impurities in other s and s–p metals. In particular, the local densities of states associated with the 3d impurities were similar to earlier work on 3d impurities in bulk Al. For spin-polarized calculations, it was found that only the alloys of V, Cr, Mn, Fe and Co with MgB2 were magnetic of all the 3d elements. It was also found that Cr and Mn in MgB2 had relatively large local magnetic moments of 2.43 and 2.87μB, respectively. The unpolarized self-consistent potentials of Mg0.97TM0.03B2 alloys, obtained within the coherent-potential approximation, were used to calculate the electron–phonon coupling constant, λ, using the Gaspari–Gyorffy formalism and the superconducting transition temperature, TC, using the Allen–Dynes equation. It was found that the calculated TC was lowest for Mg0.97Cr0.03B2 and highest for Mg0.97Zn0.03B2; in qualitative agreement with experiment. The calculated trend in variation of TC from Mn to Zn was also similar to the available experimental data. An analysis of the variation in TC, in terms of the DOS and the spectral function along the Γ to A direction, showed that the variation was an interplay between the total DOS at the Fermi energy and the creation/removal of states along the Γ to A direction.

Theoretical Study of Magnetism and Superconductivity in Three-Dimensional Transition-Metal–MgB2 Alloys. P.P.Singh, P.J.T.Joseph: Journal of Physics - Condensed Matter, 2002, 14, 12441-9