Interplay of Ferromagnetism and Superconductivity in Ni nanowires with Nb Contacts*

Combining superconductivity and spintronics effects has become a promising area for the next generation electronic devices. Owing to the mismatch of spin-spin coupling states between superconductivity and ferromagnetic materials, Cooper pairs can typically survive only a few nanometers in ferromagnetic materials. However, recent studies showed a long-range proximity effect superconductivity in a crystalline Co nanowire when capped with Pb. Meanwhile, studies showed a strong evidence for the existence of triplet superconductivity in Co-based Josephson junctions. Inspired by their works, we fabricated epitaxial Ni nanowires by CVD and magnetron sputtering deposition followed by ebeam lithography and contacted by Nb leads. RF bias cleaning was applied before Nb contacts deposition. AMR results confirm the single crystallization of Ni nanowires. The results showed that at a certain level of RF bias cleaning before Nb deposition, nanowires with gap around 500 nm between two Nb contacts exhibit zero resistance, which indicates possible supercurrent path. Furthermore, we fabricated weak-link SQUID devices by two Nb wires. The transport measurements revealed an interesting oscillatory behavior with changing applied magnetic field.