Optimizing spin-triplet supercurrent though a ferromagnetic Josephson junction

Ferromagnetic Josephson junctions show promise for application to energy efficient cryogenic memory [1]. Both spin-singlet and spin-triplet supercurrents are being studied by our group for this purpose. Engineering adjacent F layers in a three-layer system to have perpendicular magnetizations allows singlet pairs to convert to spin-aligned triplet pairs. Recent work in our group exploited a synthetic antiferromagnet (SAF) with perpendicular magnetic anisotropy (PMA) for the middle F layer [2]. These junctions exhibit phase control [2], but have a low critical current when compared to singlet junctions. To make the triplet junction a viable option for memory we show that removing the SAF while maintaining the PMA increases the critical current. To estimate the fraction of the supercurrent carried by spin-triplet pairs in our junctions, we also fabricate comparison junctions with the order of the F layers shuffled to suppress generation of spin-triplet pairs.

[1] I. Dayton, et al., IEEE Magn. Lett. 9, pp 1-5, (2018).
[2] J. A. Glick, et al., Science Advances 4, eaat9457 (2018).