We present measurements of the current-phase relation (CPR) of superconductor-ferromagnet-superconductor (SFS) Josephson junctions as a function of temperature. The CPR is determined by incorporating the junction into a superconducting loop coupled to a dc SQUID, allowing measurement of the junction phase difference. We find that the critical current of Nb-Cu 0.47Ni0.53-Nb Josephson junctions with barrier thickness ∼22 nm changes sign at T<Tπ∼2-4 K, indicating that the junction becomes a π Josephson junction. We find no evidence for second-order Josephson tunneling near Tπ in the CPR predicted by several theories.
|Original language||English (US)|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - Oct 2004|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics