Demonstrating phase control in spin-triplet ferromagnetic Josephson junctions

Ferromagnetic Josephson junctions show promise for application in 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) as the central layer. These junctions have been shown to exhibit phase control [2] but have a low critical current when compared to singlet junctions. We have shown that removing the SAF while maintaining the PMA increases the critical current by a significant amount. We demonstrate phase-control by fabricating two of these junctions in a SQUID loop, and measuring SQUID oscillations for combinations of the parallel and anti-parallel magnetic states in the two junctions.

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