In the past year, several groups have observed evidence for long-range spin-triplet supercurrent in Josephson junctions containing ferromagnetic (F) materials. In our work, the spin-triplet pair correlations are created by non-collinear magnetizations between a central Co/Ru/Co "synthetic antiferromagnet" (SAF) and two outer thin F layers. Here we present data showing that the spin-triplet supercurrent is enhanced up to 20 times after our samples are subject to a large in-plane magnetizing field. This surprising result can be explained if the Co/Ru/Co SAF undergoes a "spin-flop" transition, whereby the two Co layer magnetizations end up perpendicular to the magnetizations of the two thin F layers. Direct experimental evidence for the spin-flop transition comes from scanning electron microscopy with polarization analysis and from spin-polarized neutron reflectometry.

In the past year several groups have reported experimental evidence for spin-triplet supercurrents in Josephson junctions containing strong ferromagnetic materials. In this paper we present several new experimental results that follow up on our previous work. We study Josephson junctions of the form S/X/N/SAF/N/X/S, where S is a superconductor (Nb), N is a normal metal, SAF is a synthetic antiferromagnet of the form Co/Ru/Co and X is an ferromagnetic layer necessary to induce spin-triplet correlations in the structure. Our work is distinguished by the fact that the generation of spin-triplet correlations is tuned by the type and thickness of the X layers. The most important new result reported here is the discovery that a conventional, strong ferromagnetic material, Ni, performs well as the X layer, if it is sufficiently thin. This discovery rules out our earlier hypothesis that out-of-plane magnetocrystalline anisotropy is an important attribute of the X layers. These results suggest that the spin-triplet correlations are most likely induced by noncollinear magnetization between the X layers and adjacent Co layers. (Some figures in this article are in colour only in the electronic version) 1 To be precise, only the spin-triplet components with m s = ±1 are long range in F, where m s is the projection of the spin onto the axis of magnetization. The m s = 0 triplet component, which is always generated in S/F systems even without noncollinear magnetization, is short range in F. In this paper we always mean the m s = ±1 components when we use the term, 'spin-triplet'.

We have determined the spin-memory-loss parameter, δ Co/Ru , by measuring the transmission of spin-triplet and spin-singlet Cooper pairs across Co/Ru interfaces in Josephson junctions and by Current-Perpendicular-to-Plane Giant Magnetoresistance (CPP-GMR) techniques. The probability of spin-memory loss at the Co/Ru interface is (1 − exp(−δ Co/Ru )). From the CPP-MR, we obtain δ Co/Ru = 0.34 +0.04 −0.02 that is in good agreement with δ Co/Ru = 0.35 ± 0.08 obtained from spin-triplet transmission. For spin-singlet transmission, we have δ Co/Ru = 0.64 ± 0.05 that is different from that obtained from CPP-GMR and spin-triplet transmission. The source of this difference is not understood.