Critical Current Oscillations in Strong Ferromagnetic Pi-Junctions

TL;DR

This paper investigates Nb Josephson junctions with ferromagnetic barriers, demonstrating multiple critical current oscillations indicating 0-pi phase transitions, and shows Co barriers are promising for superconducting pi-shift devices.

Contribution

It provides experimental evidence of critical current oscillations in strongly ferromagnetic barriers and models Co barriers with existing theories, highlighting their potential for practical applications.

Findings

Multiple oscillations of critical current observed with barrier thickness.

Co barriers can be accurately modeled using existing theories.

High IcRN value in the pi-state suggests practical device potential.

Abstract

We report magnetic and electrical measurements of Nb Josephson junctions with strongly ferromagnetic barriers of Co, Ni and Ni80Fe20 (Py). All these materials show multiple oscillations of critical current with barrier thickness implying repeated 0-pi phase-transitions in the superconducting order parameter. We show in particular that the Co barrier devices can be accurately modelled using existing clean limit theories and so that, despite the high exchange energy (309 meV), the large IcRN value in the pi-state means Co barriers are ideally suited to the practical development of superconducting pi-shift devices.