Josephson tunnel junctions with a strong ferromagnetic interlayer

Abstract

The dependence of the critical current density ${j}_{c}$ on the ferromagnetic interlayer thickness ${d}_{F}$ was determined for $\text{Nb}/{\text{Al}}_{2}{\text{O}}_{3}/\text{Cu}/\text{Ni}/\text{Nb}$ Josephson tunnel junctions with ferromagnetic Ni interlayer thicknesses from very thin films $(\ensuremath{\sim}1\text{ }\text{nm})$ upward and classified into $F$-layer thickness regimes showing a dead magnetic layer, exchange, $\text{exchange}+\text{anisotropy}$ and total suppression of ${j}_{c}$. The Josephson coupling changes from 0 to $\ensuremath{\pi}$ 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 $\text{Nb}/{\text{Al}}_{2}{\text{O}}_{3}/\text{Cu}/\text{Nb}$ 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.