11 research outputs found
Planar SFS Josephson Junctions Made by Focused Ion Beam Etching
Superconductor-Ferromagnet-Superconductor (S-F-S) Josephson junctions were
fabricated by making a narrow cut through a S-F double layer using direct
writing by Focused Ion Beam (FIB). Due to a high resolution (spot size smaller
than 10 nm) of FIB, junctions with a small separation between superconducting
electrodes ( 30 nm) can be made. Such a short distance is sufficient for
achieving a considerable proximity coupling through a diluted CuNi ferromagnet.
We have successfully fabricated and studied S-F-S (Nb-CuNi-Nb) and S-S'-S
(Nb-Nb/CuNi-Nb) junctions. Junctions exhibit clear Fraunhofer modulation of the
critical current as a function of magnetic field, indicating good uniformity of
the cut. By changing the depth of the cut, junctions with the product
ranging from 0.5 mV to V were fabricated.Comment: 5 pages, 5 figures, presentation at EUCAS-2003, to be published in
Physica
Josephson Coupling and Fiske Dynamics in Ferromagnetic Tunnel Junctions
We report on the fabrication of Nb/AlO_x/Pd_{0.82}Ni_{0.18}/Nb
superconductor/insulator/ferromagnetic metal/superconductor (SIFS) Josephson
junctions with high critical current densities, large normal resistance times
area products, high quality factors, and very good spatial uniformity. For
these junctions a transition from 0- to \pi-coupling is observed for a
thickness d_F ~ 6 nm of the ferromagnetic Pd_{0.82}Ni_{0.18} interlayer. The
magnetic field dependence of the \pi-coupled junctions demonstrates good
spatial homogeneity of the tunneling barrier and ferromagnetic interlayer.
Magnetic characterization shows that the Pd_{0.82}Ni_{0.18} has an out-of-plane
anisotropy and large saturation magnetization, indicating negligible dead
layers at the interfaces. A careful analysis of Fiske modes provides
information on the junction quality factor and the relevant damping mechanisms
up to about 400 GHz. Whereas losses due to quasiparticle tunneling dominate at
low frequencies, the damping is dominated by the finite surface resistance of
the junction electrodes at high frequencies. High quality factors of up to 30
around 200 GHz have been achieved. Our analysis shows that the fabricated
junctions are promising for applications in superconducting quantum circuits or
quantum tunneling experiments.Comment: 15 pages, 9 figure
Reentrant superconducting behavior of the Josephson SFS junction. Evidence for the π-phase state
Critical supercurrents, Ic in Nb_Cu1−xNix_Nb Josephson SFS junctions with F-layers prepared from ferromagnetic Cu1−xNix alloys have been studied. For value x=0.52 and particular F-layer thickness we have observed Ic(T) oscillations with Ic vanishing for some values of T. We associate this reentrant superconducting behavior with a crossover of the SFS junction from ‘0’- to ‘π’-state that is related to temperature dependence of spatial oscillation period of induced superconducting order parameter in the weak ferromagnet. We argue this is the first experimental evidence of the π-behavior of a Josephson junction, that is the special feature of superconducting pair flow through a ferromagnet predicted for SFS junctions by Bulaevskii, Buzdin et al [1]