Anomalous Supercurrent Modulation in Josephson Junctions With Ni-Based Barriers

We investigate the supercurrent transport characteristics of Ni-barrier Josephson junctions with various barrier multilayer structures. Our device fabrication and magneto-electrical measurement methods provide high enough statistics and rigor necessary for the detailed characterization of magnetic Josephson junctions. As a result, we obtain the oscillatory critical current as a function of Ni thickness that matches the clean-limit transport theory except for certain anomalous features. Salient details include the finite oscillation phase shift due to a nonmagnetic spacer, the near-zero effective magnetic dead layer, and the distorted current-phase relationship near the 0-π transition. These allude to intricacies in the microscopic transport that are unique to certain magnetic Josephson junctions. We discuss a route toward a comprehensive understanding of realistic magnetic Josephson junctions based on the underlying effect of exchange field on the superconducting spin modulation.