Josephson tunnel junctions with strong ferromagnetic interlayer

TL;DR

This study investigates how the critical current density in Nb/Al2O3/Cu/Ni/Nb Josephson junctions varies with ferromagnetic Ni interlayer thickness, revealing different magnetic regimes and the impact on supercurrent behavior.

Contribution

It provides detailed experimental analysis of the critical current dependence on Ni interlayer thickness, including the transition from 0 to pi coupling and interface scattering effects.

Findings

Critical current density varies with Ni thickness, showing distinct magnetic regimes.

Transition from 0 to pi Josephson coupling as a function of interlayer thickness.

Strong supercurrent suppression due to interface scattering in ferromagnetic layers.

Abstract

The dependence of the critical current density j_c on the ferromagnetic interlayer thickness d_F was determined for Nb/Al_2O_3/Cu/Ni/Nb Josephson tunnel junctions with ferromagnetic \Ni interlayer from very thin film thicknesses (\sim 1 nm) upwards 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 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 non-magnetic \Nb/Al_2O_3/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 theory were carried out, indicating dirty limit condition, too. The results were discussed in the framework of literature