Cr/Fe and Pt/Co spin-mixer interfaces for spin-aligned triplet Cooper pair creation

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Interfaces between superconductors and ferromagnets host rich physical phenomena which may find applications in low-energy computing. This is the aim of the emerging field of superconducting spintronics. This work focuses on the fabrication of nanopillar Josephson junctions which include a ferromagnetic layer and a spin-mixer in order to investigate the generation of a long-range triplet component (LRTC) of the supercurrent. A spin-glass is predicted to arise at a Cr/Fe interface [1], which provides the magnetic inhomogeneity required to generate a LRTC. It has recently been proposed that spin-orbit coupling (SOC) may substitute the role of the magnetic inhomogeneity in interconverting the triplet states [2,3]; to investigate this we fabricate devices with Pt/Co interfaces. The SOC arises from the high atomic number of Pt and broken inversion symmetry at its interfaces, and is of pure Rashba type. Furthermore, it has been shown experimentally that interfacing a superconductor with a large SOC material enhances spin transport through the superconductor [4]; hence the combination of Fe/Cr based devices with an additional thin Pt layer is explored.[1] Robinson, J. W. A., Banerjee, N., & Blamire, M. G. 104505, 1-4 (2014). [2] Bergeret, F. S., & Tokatly, I. V. Phys. Rev. B 89(13), 1-13 (2014). [3] Jacobsen, S., Kulagina, I., & Linder, J. Sci. Rep. 6:23926 (2015).[4] Jeon, K.-R. et al. Nat. Mater. 17, 499 (2018).