Effect of Interfaces on Supercurrent Through Ferromagnetic Materials

Ferromagnetic Josephson junctions exhibit fascinating physics and the potential for applications in superconducting logic and memory. The junctions in a demonstrated superconducting memory prototype contain a magnetic spin-valve structure with Ni as the fixed layer and NiFe (Permalloy) as the free layer. However, NiFe exhibits poor supercurrent transmission, which limits the efficiency of the Josephson junction. We have previously shown that the supercurrent transmission through a Cu/NiFe/Cu trilayer can be improved by adding thin layers of Ni between the Cu and NiFe—– possibly due to the advantageous spin-dependent transport properties of the Cu/Ni interfaces. In this work, we explore this idea further by replacing the Cu/NiFe interfaces with Pd/NiFe, which also have more desirable transport properties. Compared to the reference junctions containing Cu/NiFe interfaces, the new junctions exhibit an increase in the
$\pi$
-state supercurrent by a factor of 2 along with a change in the position of the first
$0-\pi$
transition.