Magnetic barrier structures for superconductingmagnetic hybrid Josephson junctions

If Josephson and spintronic technologies can be successfully integrated to produce a cryogenic memory that can be controlled with single-flux quantum pulses, then they may enable ultra-low-power, high-speed computing. We have developed hybrid Josephson junctions with Nb electrodes, using barrier materials composed of both pseudo-spin valves (PSV) and magnetic-clusters. Our choice of relatively weak ferromagnetic materials such as Ni, PdFe, and NiFeNb enabled us to grow individual layers beyond a few monolayers such that the junctions made with these materials exhibit Josephson coupling as well as magnetic switching behavior. The differences in switching field of each layer were determined by magnetization measurements at 10 K. We fabricated junctions with a wide range of areas (1 μm² to 100 μm²) by high-throughput, conventional fabrication techniques. In PSV-barrier junctions, the critical current is strongly modulated by the magnetic state in the barrier, including magnetic hysteresis. In junctions with Mn-doped Si barriers, the Josephson coupling was tuned by the density of the Mn magnetic-clusters. Such devices may offer an energy-efficient way to control Josephson junction properties by changing their collective states.