Spin Fluctuations Associated with the Formation of Localized Magnetic Moments in Superconductors

A new theory of superconductors containing transition-metal impurities is presented, explaining the observed anomalous magnetic behavior of the impurities with quenched or nearly quenched magnetic moment resulting from the localized spin fluctuations associated with the formation of localized magnetic moments. From this theory, the superconducting transition temperatures of $\mathrm{Al}\mathrm{Mn}$, $\mathrm{Al}\mathrm{Cr}$, and $V\mathrm{Fe}$ are calculated. The puzzling "slowing down" of the decrease in $T_c$ observed for higher concentrations of transition-metal impurities is shown to arise partly from the temperature dependence of the electron scattering by the localized spin fluctuations and also partly from exchange and Coulomb coupling among the transition-metal impurities, which damp the formation of the localized magnetic moments and the spin fluctuations.