Josephson tunnel junctions with a strong ferromagnetic interlayer

The dependence of the critical current density j_c on the ferromagnetic interlayer thickness d_F was determined for Nb/Al₂O₃/Cu/Ni/Nb Josephson tunnel junctions with ferromagnetic Ni interlayer thicknesses from very thin films (∼1nm) upward and classified into F -layer thickness regimes showing a dead magnetic layer, exchange, exchange+anisotropy and total suppression of j_c . The Josephson coupling changes from 0 to π as function of d_F , and—very close to the crossover thickness—as function of temperature. The strong suppression of the supercurrent in comparison to nonmagnetic Nb/Al₂O₃/Cu/Nb junctions indicated that the insertion of a F layer leads to additional interface scattering. The transport inside the dead magnetic layer was in dirty limit. For the magnetically active regime fitting with both the clean and the dirty limit theories was carried out, indicating dirty limit condition, too. The results were discussed in the framework of literature.