Josephson junctions containing Ni/Ru/Ni synthetic antiferromagnets

Ferromagnetic Josephson junctions with reliable control over the ground-state phase difference have applications in cryogenic memory. Phase control has been successfully demonstrated with devices containing a Ni fixed layer and a NiFe free layer [1,2]. However, the magnetic reliability and critical current magnitude of these junctions need to be improved. One idea is to replace the thin Ni fixed layer with a thicker unbalanced Ni/Ru/Ni synthetic antiferromagnet (SAF). In this work, we take the first step and measure supercurrent transmission through balanced Ni/Ru/Ni SAFs [3]. We observe that the supercurrent decays remarkably slowly, suggesting that the transport through the SAFs could be partially ballistic.

[1] E. C. Gingrich, B. M. Niedzielski, J. A. Glick, Y. Wang, D. L. Miller, R. Loloee, W. P. Pratt, and N. O. Birge, Nat. Phys. 12, 564 (2016).

[2] I. Dayton, T. Sage, E. Gingrich, M. Loving, T. Ambrose, N. Siwak, S. Keebaugh, C. Kirby, D. Miller, A. Herr, Q. Herr, and O. Naaman, IEEE Magn. Lett. 9, 3301905 (2018).

[3] S.S. Mishra, R. Loloee, and N.O. Birge. "Supercurrent transmission through Ni/Ru/Ni synthetic antiferromagnets." arXiv:2108.10376 (2021).