188 research outputs found
Stray field and superconducting surface spin valve effect in LaCaMnO/YBaCuO bilayers
Electronic transport and magnetization measurements were performed on
LaCaMnO/YBaCuO (LCMO/YBCO) bilayers
below the superconducting transition temperature in order to study the
interaction between magnetism and superconductivity. This study shows that a
substantial number of weakly pinned vortices are induced in the YBCO layer by
the large out-of-plane stray field in the domain walls. Their motion gives rise
to large dissipation peaks at the coercive field. The angular dependent
magnetoresistance (MR) data reveal the interaction between the stripe domain
structure present in the LCMO layer and the vortices and anti-vortices induced
in the YBCO layer by the out-of-plane stray field. In addition, this study
shows that a superconducting surface spin valve effect is present in these
bilayers as a result of the relative orientation between the magnetization at
the LCMO/YBCO interface and the magnetization in the interior of the LCMO layer
that can be tuned by the rotation of a small . This latter finding will
facilitate the development of superconductive magnetoresistive memory devices.
These low-magnetic field MR data, furthermore, suggest that triplet
superconductivity is induced in the LCMO layer, which is consistent with recent
reports of triplet superconductivity in LCMO/YBCO/LCMO trilayers and LCMO/YBCO
bilayers.Comment: 14 pages, 3 figure
Anomalous Paramagnetic Magnetization in Mixed State of CeCoIn single crystals
Magnetization and torque measurements were performed on CeCoIn single
crystals to study the mixed-state thermodynamics. These measurements allow the
determination of both paramagnetic and vortex responses in the mixed-state
magnetization. The paramagnetic magnetization is suppressed in the mixed state
with the spin susceptibility increasing with increasing magnetic field. The
dependence of spin susceptibility on magnetic field is due to the fact that
heavy electrons contribute both to superconductivity and paramagnetism and a
large Zeeman effect exists in this system. No anomaly in the vortex response
was found within the investigated temperature and field range
Pairing Symmetry of CeCoIn Detected by In-plane Torque Measurements
In-plane torque measurements were performed on heavy fermion CeCoIn
single crystals in the temperature range 1.8 K K and
applied magnetic field up to 14 T. The normal-state torque is given by
. The reversible part of the
mixed-state torque, obtained after subtracting the corresponding normal state
torque, shows also a four-fold symmetry. In addition, sharp peaks are present
in the irreversible torque at angles of 4, 3/4, 5/4, 7/4,
etc. Both the four-fold symmetry in the reversible torque and the sharp peaks
in the irreversible torque of the mixed state imply symmetry of the
superconducting order parameter. The field and temperature dependences of the
reversible mixed-state torque provide further evidence for wave
symmetry. The four-fold symmetry in the normal state has a different origin
since it has different field and temperature dependences than the one in the
mixed state. The possible reasons of the normal state four-fold symmetry are
discussed
Orbital and Pauli limiting effects in heavily doped BaKFeAs
We investigated the thermodynamic properties of the Fe-based lightly
disordered superconductor BaKFeAs in external
magnetic field H applied along the FeAs layers (H//ab planes). The
superconducting (SC) transition temperature for this doping level is T =
6.6 K. Our analysis of the specific heat C(T,H) measured for T < T implies
a sign change of the superconducting order parameter across different Fermi
pockets. We provide experimental evidence for the three components
superconducting order parameter. We find that all three components have values
which are comparable with the previously reported ones for the stochiometric
compound KFeAs. Our data for C(T,H) and resistivity rho(T,H) can be
interpreted in favor of the dominant orbital contribution to the pair-breaking
mechanism at low fields, while Pauli limiting effect dominates at high fields,
giving rise to a gapless superconducting state with only the leading non-zero
gap.Comment: 7 pages, 5 figure
Strong magnetic fluctuations in superconducting state of CeCoIn
We show results on the vortex core dissipation through current-voltage
measurements under applied pressure and magnetic field in the superconducting
phase of CeCoIn. We find that as soon as the system becomes
superconducting, the vortex core resistivity increases sharply as the
temperature and magnetic field decrease. The sharp increase in flux flow
resistivity is due to quasiparticle scattering on critical antiferromagnetic
fluctuations. The strength of magnetic fluctuations below the superconducting
transition suggests that magnetism is complimentary to superconductivity and
therefore must be considered in order to fully account for the low-temperature
properties of CeCoIn.Comment: 7 pages, 6 figure
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