5,001 research outputs found
Vortex Softening: Origin of the second peak effect in BiSrCaCuO
Transverse ac permeability measurements in BiSrCaCuO single crystals at low fields and temperatures in a vortex configuration
free of external forces show that the decrease of the critical current as
measured by magnetization loops at the second peak effect is an artifact due to
creep. On the other hand, the increase of critical current at the second peak
is due to a genuine softening of the tilting elastic properties of vortices in
the individual pinning regime that precedes the transition to a disorder state.Comment: 4 pages, 5 figures, RevTex, two column versio
Remarkable magnetostructural coupling around the magnetic transition in CeCoFeSi
We report a detailed study of the magnetic properties of
CeCoFeSi under high magnetic fields (up to 16 Tesla)
measuring different physical properties such as specific heat, magnetization,
electrical resistivity, thermal expansion and magnetostriction.
CeCoFeSi becomes antiferromagnetic at 6.7 K.
However, a broad tail (onset at 13 K) in the specific heat
precedes that second order transition. This tail is also observed in the
temperature derivative of the resistivity. However, it is particularly
noticeable in the thermal expansion coefficient where it takes the form of a
large bump centered at . A high magnetic field practically washes out that
tail in the resistivity. But surprisingly, the bump in the thermal expansion
becomes a well pronounced peak fully split from the magnetic transition at
. Concurrently, the magnetoresistance also switches from negative to
positive just below . The magnetostriction is considerable and
irreversible at low temperature (
410 at 2 K) when the magnetic interactions dominate. A broad
jump in the field dependence of the magnetostriction observed at low may be
the signature of a weak ongoing metamagnetic transition. Taking altogether, the
results indicate the importance of the lattice effects in the development of
the magnetic order in these alloys.Comment: 5 pages, 6 figure
Nonlinear Supersymmetry as a Hidden Symmetry
Ver abstrac
Enhanced weak superconductivity in trigonal -PtBi
Electrical transport experiments show superconductivity in a high-quality
single crystal of trigonal -PtBi. The critical temperature shows a
large dependence on the electrical current and in the limit of very low
currents, a = 1.1 K is observed, while a zero temperature critical field
(0) 1.5 Tesla is estimated. These are the highest
superconducting parameters reported (at ambient pressure) in a stoichiometric
-PtBi bulk sample so far. Under a magnetic field a strict zero
resistance state is no longer observed even though an incipient superconducting
transition is seen. Such a behavior is most probably associated with very low
critical currents and is reminiscent of filamentary superconductivity. The
superconducting state is elusive to magnetization measurements discarding a
bulk phase down to 0.3 K.Comment: 5 pages, 5 figure
High magnetic field thermal-expansion and elastic properties of CeRhIn
We report high magnetic field thermal-expansion and magnetostriction results
on CeRhIn single crystals. Several transitions, both first and second
order, are observed when the field is applied perpendicular to the
crystallographic c-axis. The magnetic field dependence of the thermal-expansion
coefficient above 15 K, where the magnetic correlations are negligible, can be
explained supposing an almost pure ground state doublet, in
apparent contradiction with neutron scattering experiments. Although the
spin-lattice interaction is relevant in this compound, the effect of the
magnetic correlations on the elastic properties is relatively weak, as revealed
by resonant ultrasound spectroscopy experiments.Comment: 5 pages, 6 figure
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