On the Coexistence of Superconductivity and Ferromagnetism

The effect of the dynamical nature of impurity spins on the superconducting transition is studied in dilute alloys with the paramagnetic impurities which are ordered ferromagnetically. Only the exchange interaction between electrons and impurity spins is considered, and, by taking terms up to second order in this interaction, the possibility of coexistence of superconductivity and ferromagnetism is studied. The dynamical nature of the impurity spins is shown to have a rather large effect on the superconducting transition in the ferromagnetic state, and the coexistence of the two phases becomes possible at least for a ferromagnetic exchange interaction.