1,020 research outputs found
Visualizing supercurrents in ferromagnetic Josephson junctions with various arrangements of 0 and \pi segments
Josephson junctions with ferromagnetic barrier can have positive or negative
critical current depending on the thickness of the ferromagnetic layer.
Accordingly, the Josephson phase in the ground state is equal to 0 (a
conventional or 0 junction) or to ( junction). When 0 and
segments are joined to form a "0- junction", spontaneous supercurrents
around the 0- boundary can appear. Here we report on the visualization of
supercurrents in superconductor-insulator-ferromagnet-superconductor (SIFS)
junctions by low-temperature scanning electron microscopy (LTSEM). We discuss
data for rectangular 0, , 0-, 0--0 and 20 \times 0-
junctions, disk-shaped junctions where the 0- boundary forms a ring, and
an annular junction with two 0- boundaries. Within each 0 or segment
the critical current density is fairly homogeneous, as indicated both by
measurements of the magnetic field dependence of the critical current and by
LTSEM. The parts have critical current densities up to
35\units{A/cm^2} at T = 4.2\units{K}, which is a record value for SIFS
junctions with a NiCu F-layer so far. We also demonstrate that SIFS technology
is capable to produce Josephson devices with a unique topology of the 0-
boundary.Comment: 29 pages, 8 figure
Interference patterns of multifacet 20x(0-pi-) Josephson junctions with ferromagnetic barrier
We have realized multifacet Josephson junctions with periodically alternating
critical current density (MJJs) using
superconductor-insulator-ferromagnet-superconductor heterostructures. We show
that anomalous features of critical current vs. applied magnetic field,
observed also for other types of MJJs, are caused by a non-uniform flux density
(parallel to the barrier) resulting from screening currents in the electrodes
in the presence of a (parasitic) off-plane field component.Comment: submitted to PR
Suppression of dissipation in Nb thin films with triangular antidot arrays by random removal of pinning sites
The depinning current Ic versus applied magnetic field B close to the
transition temperature Tc of Nb thin films with randomly diluted triangular
arrays of antidots is investigated. % Our experiments confirm essential
features in Ic(B) as predicted by Reichhardt and Olson Reichhardt [Phys.Rev. B
76, 094512 (2007)]. % We show that, by introducing disorder into periodic
pinning arrays, Ic can be enhanced. % In particular, for arrays with fixed
density n_p of antidots, an increase in dilution Pd induces an increase in Ic
and decrease of the flux-flow voltage for B>Bp=n_p Phi_0.Comment: 5 pages, 4 figure
Transport, magnetic, and structural properties of LaCeMnO thin films. Evidence for hole-doping
Cerium-doped manganite thin films were grown epitaxially by pulsed laser
deposition at C and oxygen pressure Pa and were
subjected to different annealing steps. According to x-ray diffraction (XRD)
data, the formation of CeO as a secondary phase could be avoided for
Pa. However, transmission electron microscopy shows the presence
of CeO nanoclusters, even in those films which appear to be single phase in
XRD. With O annealing, the metal-to-insulator transition temperature
increases, while the saturation magnetization decreases and stays well below
the theoretical value for electron-doped LaCeMnO with mixed
Mn/Mn valences. The same trend is observed with decreasing film
thickness from 100 to 20 nm, indicating a higher oxygen content for thinner
films. Hall measurements on a film which shows a metal-to-insulator transition
clearly reveal holes as dominating charge carriers. Combining data from x-ray
photoemission spectroscopy, for determination of the oxygen content, and x-ray
absorption spectroscopy (XAS), for determination of the hole concentration and
cation valences, we find that with increasing oxygen content the hole
concentration increases and Mn valences are shifted from 2+ to 4+. The
dominating Mn valences in the films are Mn and Mn, and only a
small amount of Mn ions can be observed by XAS. Mn and Ce
XAS signals obtained in surface-sensitive total electron yield mode are
strongly reduced in the bulk-sensitive fluorescence mode, which indicates
hole-doping in the bulk for those films which do show a metal-to-insulator
transition.Comment: 8 pages, 10 figure
Crossover between different regimes of inhomogeneous superconductivity in planar superconductor-ferromagnet hybrids
We studied experimentally the effect of a stripe-like domain structure in a
ferromagnetic BaFe_{12}O_{19} substrate on the magnetoresistance of a
superconducting Pb microbridge. The system was designed in such a way that the
bridge is oriented perpendicular to the domain walls. It is demonstrated that
depending on the ratio between the amplitude of the nonuniform magnetic field
B_0, induced by the ferromagnet, and the upper critical field H_{c2} of the
superconducting material, the regions of the reverse-domain superconductivity
in the H-T plane can be isolated or can overlap (H is the external magnetic
field, T is temperature). The latter case corresponds to the condition
B_0/H_{c2}<1 and results in the formation of superconductivity above the
magnetic domains of both polarities. We discovered the regime of edge-assisted
reverse-domain superconductivity, corresponding to localized superconductivity
near the edges of the bridge above the compensated magnetic domains. Direct
verification of the formation of inhomogeneous superconducting states and
external-field-controlled switching between normal state and inhomogeneous
superconductivity were obtained by low-temperature scanning laser microscopy.Comment: 11 pages, 12 figure
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