We have studied in detail and extended the recent theory of Gor'kov and Rusinov which describes superconductors with ferromagnetically aligned impurities, under the assumption that the electron mean free path due to spin-orbit interaction is small as compared with the coherence distance. We show that all usually considered physical quantities of such a system are identical to those of a superconductor containing magnetic impurities with randomly oriented spins, and point out those vertices for which differences should arise. In addition, we investigate the magnetic properties of such systems. The upper critical field as a function of impurity concentration and temperature is calculated, and it is shown that the specific heat at the transition point in the presence of a field is a function of temperature only and does not depend on the magnetic-impurity concentration. The last results can explain the recent experimental findings by Finnemore et al.

• Received 23 August 1965

DOI:https://doi.org/10.1103/PhysRev.141.275