Superconductivity and magnetic order in ferromagnets and spin-glasses

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Abstract
Taking into account the effect of both time and spatial-dependent correlations of the magnetic impurities on pair breaking, we derive an expression for the superconducting transition temperature. Ferromagnets and spin-glasses are discussed. We find, in agreement with previous workers, that spatial correlations which are ferromagnetic have a tendency to enhance the pair breaking effect, while spatial correlations for an antiferromagnet or spin-glass reduce the pair breaking. However, we find that the introduction of dynamics (time correlations) always reduces the pair breaking for all types of magnetic ordering. In particular, for the spin-glass case we found that the time correlations give rise to a "re-entrant" phenomena.