207 research outputs found
Direct measurements of the penetration depth in a superconducting film using magnetic force microscopy
We report the local measurements of the magnetic penetration depth
in a superconducting Nb film using magnetic force microscopy (MFM). We
developed a method for quantitative extraction of the penetration depth from
single-parameter simultaneous fits to the lateral and height profiles of the
MFM signal, and demonstrate that the obtained value is in excellent agreement
with that obtained from the bulk magnetization measurements.Comment: 3 pages, 4 figures, submitted to APL on 08/18/0
Strong Enhancement of the Critical Current at the Antiferromagnetic Transition in ErNi2B2C Single Crystals
We report on transport and magnetization measurements of the critical current
density Jc in ErNi2B2C single crystals that show strongly enhanced vortex
pinning at the Neel temperature TN and low applied fields. The height of the
observed Jc peak decreases with increasing magnetic field in clear contrast
with that of the peak effect found at the upper critical field. We also
performed the first angular transport measurements of Jc ever conducted on this
compound. They reveal the correlated nature of this pinning enhancement, which
we attribute to the formation of antiphase boundaries at TN.Comment: 3 figure
The influence of structural defects on intra-granular critical currents of bulk MgB2
Bulk MgB2 samples were prepared under different synthesis conditions and
analyzed by scanning and transmission electron microscopy. The critical current
densities were determined from the magnetization versus magnetic field curves
of bulk and powder-dispersed-in-epoxy samples. Results show that through a slow
cooling process, the oxygen dissolved in bulk MgB2 at high synthesis
temperatures can segregate and form nanometer-sized coherent precipitates of
Mg(B,O)2 in the MgB2 matrix. Magnetization measurements indicate that these
precipitates act as effective flux pinning centers and therefore significantly
improve the intra-grain critical current density and its field dependence.Comment: 4 pages, 4 figures, to be published in IEE Transactions in Applied
Superconductivit
Large magnetic penetration depth and thermal fluctuations in a Ca(PtAs)[(FePt)As] (x=0.097) single crystal
We have measured the temperature dependence of the absolute value of the
magnetic penetration depth in a
Ca(PtAs)[(FePt)As] (x=0.097)
single crystal using a low-temperature magnetic force microscope (MFM). We
obtain (0)1000 nm via extrapolating the data to .
This large and pronounced anisotropy in this system are responsible
for large thermal fluctuations and the presence of a liquid vortex phase in
this low-temperature superconductor with critical temperature of 11 K,
consistent with the interpretation of the electrical transport data. The
superconducting parameters obtained from and coherence length
place this compound in the extreme type \MakeUppercase{\romannumeral 2} regime.
Meissner responses (via MFM) at different locations across the sample are
similar to each other, indicating good homogeneity of the superconducting state
on a sub-micron scale
The Effect of Splayed Pins on Vortex Creep and Critical Currents
We study the effects of splayed columnar pins on the vortex motion using
realistic London Langevin simulations. At low currents vortex creep is strongly
suppressed, whereas the critical current j_c is enhanced only moderately.
Splaying the pins generates an increasing energy barrier against vortex
hopping, and leads to the forced entanglement of vortices, both of which
suppress creep efficiently. On the other hand splaying enhances kink nucleation
and introduces intersecting pins, which cut off the energy barriers. Thus the
j_c enhancement is strongly parameter sensitive. We also characterize the angle
dependence of j_c, and the effect of different splaying geometries.Comment: 4 figure
Depinning of a superfluid vortex line by Kelvin waves
We measure the interaction of a single superfluid vortex with surface
irregularities. While vortex pinning in superconductors usually becomes weaker
at higher temperatures, we find the opposite behavior. The pinning steadily
increases throughout our measurement range, from 0.15Tc to over 0.5Tc. We also
find that moving the other end of the vortex decreases the pinning, so we
propose Kelvin waves along the vortex as a depinning mechanism.Comment: 5 figures; substantial revision including 2 new figure
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