The dependence of the superconducting critical temperature of dilute magnetic alloys on impurity concentration

The decrease in superconducting critical temperature T c with impurity concentration n I is examined for dilute magnetic alloys in the framework of the Kondo-Nagaoka theory. When the critical temperature T co of the host metal is much larger than the Kondo temperature T K the curves of T c versus n I behave in the manner predicted by the Born approximation theory of Abrikosov and Gorkov, except for an exponential tail for T c << T K . When T co << T K these curves show a non-magnetic behaviour which is related to the theory of the Suhl-Nagaoka spin compensated state. The theory is compared to (i) experimental data for La Ce and Th U and (ii) the theory of localized spin fluctuations which provides an alternative explanation for the data.