SFS Josephson Junctions using PdNi alloy

We have studied the variation of critical current in Superconductor/Ferromagnet/Superconductor (S/F/S) Josephson Junctions as a function of ferromagnet thickness (d$_{F})$ using a weakly ferromagnetic alloy, Pd$_{82}$Ni$_{12}$. The critical current density oscillates and decays over five orders of magnitude as d$_{F}$ is increased from 32 to 100 nm. These oscillations are indicative of 0-$\pi $ transitions in S/F/S junctions. We find the characteristic length of oscillation ($\xi _{F2} )$ to be 4.3 $\pm $ 0.1 nm and the characteristic length of decay ($\xi _{F1} )$ to be 7.9 $\pm $ 0.4 nm. Earlier studies [1] using a similar PdNi alloy in S/I/F/S junctions found $\xi _{F1} \approx \xi _{F2} \approx 2.8{\kern 1pt}nm$, however, those measurements were performed for d$_{F}$ between 4.5 and 14 nm. In our experiment, $\xi _{F1} >\xi _{F2} $, indicating that our samples are in the regime $E_{ex} \tau >\hbar $ [2, 3], where E$_{ex}$ is the exchange energy and $\tau $ is the mean free time between electron collisions in the ferromagnet. In spite of covering this wide range, we see no evidence of a crossover to a slower decay, which, if present, would be indicative of long-range spin triplet correlations [4]. [1] T. Kontos et al.,Phys. Rev. Lett. 89, 137007 (2002). [2] F. S. Bergeret, et al., Phys. Rev. B, 64, 134506 (2001) [3] Kashuba, et al., Phys. Rev. B. 75, 132502 (2007). [4] F.S. Bergeret, et al., Rev. Mod. Phys. 77, 1321 (2005). [This work is supported by US-DOE grant, DE-FG02-06ER46341.]