Ferromagnetic Josephson junctions with perpendicular magnetic anisotropy

Ferromagnetic Josephson junctions are a strong candidate to become a dissipationless cryogenic memory alternative to dissipative CMOS technologies. In order to build such a memory, the ferromagnetic Josephson junctions must be optimised for both the switching of the ferromagnetic layer and the critical current of the junction. The critical current of the junction decays exponentially with the ferromagnet thickness, making a thin ferromagnet preferable, however typically for in-plane ferromagnets the switching properties worsen as the ferromagnet is thinned. In addition, stray fields from an in-plane ferromagnet add a vector potential in the Josephson junction. To solve these issues, here we explore the use of ferromagnets with perpendicular magnetic anisotropy. We find that, unlike for in-plane ferromagnets, the switching properties of Co in a Nb-Pt-Co(d_Co)-Pt-Nb wedge are optimised for ultra-thin (≤0.6 nm) films. We will also report our progress characterising Josephson junctions with perpendicular Co and CoB ferromagnetic layers.