Resistance oscillations in junctions of superconductor–magnetic system

Resistance oscillations as a function of magnetic field were observed in superconductor–magnetic tunnel junctions of Nb–Fe–FeOx–SiO2–Au–Nb. Junctions involving superconductor–magnetic layer superconductor system are exciting because for certain regime of ferromagnetic layer thickness, a Josephson coupling with an intrinsic phase difference of π might be stabilized. For fabrication of the tunnel junctions the thin films were deposited by RF/DC magnetron sputtering. Using photolithography and reactive ion etching, square junctions of size varying from 50μm to 250μm were defined. I–V characteristics and R vs. H characteristics were studied at 4.2K. When the magnetic field is applied parallel to the junction plane, measurements of the junction resistance as a function of magnetic field at a fixed temperature show resistance peaks whenever the total magnetic flux through the junction equals an integral multiple of flux quantum. The penetration depth of the superconducting electrodes was estimated from the positions of the resistance peaks.