3,422 research outputs found
Unanticipated proximity behavior in ferromagnet-superconductor heterostructures with controlled magnetic noncollinearity
Magnetization noncollinearity in ferromagnet-superconductor (F/S)
heterostructures is expected to enhance the superconducting transition
temperature (Tc) according to the domain-wall superconductivity theory, or to
suppress Tc when spin-triplet Cooper pairs are explicitly considered. We study
the proximity effect in F/S structures where the F layer is a Sm-Co/Py
exchange-spring bilayer and the S layer is Nb. The exchange-spring contains a
single, controllable and quantifiable domain wall in the Py layer. We observe
an enhancement of superconductivity that is nonmonotonic as the Py domain wall
is increasingly twisted via rotating a magnetic field, different from
theoretical predictions. We have excluded magnetic fields and vortex motion as
the source of the nonmonotonic behavior. This unanticipated proximity behavior
suggests that new physics is yet to be captured in the theoretical treatments
of F/S systems containing noncollinear magnetization.Comment: 17 pages, 4 figures. Physical Review Letters in pres
Test beam Characterizations of 3D Silicon Pixel detectors
3D silicon detectors are characterized by cylindrical electrodes
perpendicular to the surface and penetrating into the bulk material in contrast
to standard Si detectors with planar electrodes on its top and bottom. This
geometry renders them particularly interesting to be used in environments where
standard silicon detectors have limitations, such as for example the radiation
environment expected in an LHC upgrade. For the first time, several 3D sensors
were assembled as hybrid pixel detectors using the ATLAS-pixel front-end chip
and readout electronics. Devices with different electrode configurations have
been characterized in a 100 GeV pion beam at the CERN SPS. Here we report
results on unirradiated devices with three 3D electrodes per 50 x 400 um2 pixel
area. Full charge collection is obtained already with comparatively low bias
voltages around 10 V. Spatial resolution with binary readout is obtained as
expected from the cell dimensions. Efficiencies of 95.9% +- 0.1 % for tracks
parallel to the electrodes and of 99.9% +- 0.1 % at 15 degrees are measured.
The homogeneity of the efficiency over the pixel area and charge sharing are
characterized.Comment: 5 pages, 7 figure
Surface spin-flop transition in a uniaxial antiferromagnetic Fe/Cr superlattice induced by a magnetic field of arbitrary direction
We studied the transition between the antiferromagnetic and the surface
spin-flop phases of a uniaxial antiferromagnetic [Fe(14 \AA)/Cr(11 \AA] superlattice. For external fields applied parallel to the in-plane easy
axis, the layer-by-layer configuration, calculated in the framework of a
mean-field one-dimensional model, was benchmarked against published polarized
neutron reflectivity data. For an in-plane field applied at an angle with the easy axis, magnetometry shows that the magnetization
vanishes at H=0, then increases slowly with increasing . At a critical value
of , a finite jump in is observed for , while a
smooth increase of is found for . A dramatic
increase in the full width at half maximum of the magnetic susceptibility is
observed for . The phase diagram obtained from
micromagnetic calculations displays a first-order transition to a surface
spin-flop phase for low values, while the transition becomes continuous
for greater than a critical angle, . This is in fair agreement with the experimentally observed results.Comment: 24 pages, 7 figure
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