Spin-triplet supercurrent in Co/Ni multilayer Josephson junctions with perpendicular anisotropy

Abstract

We have measured spin-triplet supercurrent in Josephson junctions of the form S/${\text{F}}^{\ensuremath{'}}$/F/${\text{F}}^{\ensuremath{'}}$/S, where S is superconducting Nb, ${\text{F}}^{\ensuremath{'}}$ is a thin Ni layer with in-plane magnetization, and F is a Ni/[Co/Ni]${}_{n}$ multilayer with out-of-plane magnetization. The supercurrent in these junctions decays very slowly with F-layer thickness and is much larger than in similar junctions not containing the two ${\text{F}}^{\ensuremath{'}}$ layers. Those two features are the characteristic signatures of spin-triplet supercurrent, which is maximized by the orthogonality of the magnetizations in the F and ${\text{F}}^{\ensuremath{'}}$ layers. Magnetic measurements confirm the out-of-plane anisotropy of the Co/Ni multilayers. These samples have their critical current optimized in the as-prepared state, which will be useful for future applications.