13 research outputs found
Effect of sintering temperature under high pressure in the uperconductivity for MgB2
We report the effect of the sintering temperature on the superconductivity of
MgB2 pellets prepared under a high pressure of 3 GPa. The superconducting
properties of the non-heated MgB2 in this high pressure were poor. However, as
the sintering temperature increased, the superconducting properties were vastly
enhanced, which was shown by the narrow transition width for the resistivity
and the low-field magnetizations. This shows that heat treatment under high
pressure is essential to improve superconducting properties. These changes were
found to be closely related to changes in the surface morphology observed using
scanning electron microscopy.Comment: 3 Pages including 3 figure
Microstructure and pinning properties of hexagonal-disc shaped single crystalline MgB2
We synthesized hexagonal-disc-shaped MgB2 single crystals under high-pressure
conditions and analyzed the microstructure and pinning properties. The lattice
constants and the Laue pattern of the crystals from X-ray micro-diffraction
showed the crystal symmetry of MgB2. A thorough crystallographic mapping within
a single crystal showed that the edge and c-axis of hexagonal-disc shape
exactly matched the (10-10) and the (0001) directions of the MgB2 phase. Thus,
these well-shaped single crystals may be the best candidates for studying the
direction dependences of the physical properties. The magnetization curve and
the magnetic hysteresis for these single crystals showed the existence of a
wide reversible region and weak pinning properties, which supported our single
crystals being very clean.Comment: 5 pages, 3 figures. submitted to Phys. Rev.
High current-carrying capability in c-axis-oriented superconducting MgB2 thin films
In high-quality c-axis-oriented MgB2 thin films, we observed high critical
current densities (Jc) of 16 MA/cm^2 at 15 K under self fields comparable to
those of cuprate high-temperature superconductors. The extrapolated value of Jc
at 5 K was estimated to be 40 MA/cm^2. For a magnetic field of 5 T, a Jc of 0.1
MA/cm^2 was detected at 15 K, suggesting that this compound would be a very
promising candidate for practical applications at high temperature and lower
power consumption. The vortex-glass phase is considered to be a possible
explanation for the observed high current-carrying capability.Comment: 3 pages and 4 figures, to be published in Physical Review Letter
Prominent bulk pinning effect in the MgB_2 superconductor
We report the magnetic-field dependence of the irreversible magnetization of
the recently discovered binary superconductor MgB. For the temperature
region of , the contribution of the bulk pinning to the
magnetization overwhelms that of the surface pinning. This was evident from the
fact that the magnetization curves, , were well described by the
critical-state model without considering the surface pinning effect. It was
also found that the curves at various temperatures scaled when the field
and the magnetization were normalized by the characteristic scaling factors
and , respectively. This feature suggests that the
pinning mechanism determining the hysteresis in is unique below .Comment: 4pages and 4 figures. Phys. Rev. B (accepted
Universal scaling of the Hall resistivity in MgB2 superconductors
The mixed-state Hall resistivity and the longitudinal resistivity in
superconducting MgB2 thin films have been investigated as a function of the
magnetic field over a wide range of current densities from 100 to 10000 A/cm^2.
We observe a universal Hall scaling behavior with a constant exponent of 2.0,
which is independent of the magnetic field, the temperature, and the current
density. This result can be interpreted well within the context of recent
theories.Comment: 4 page
Critical flux pinning and enhanced upper-critical-field in magnesium diboride films
We have conducted pulsed transport measurements on c-axis oriented magnesium
diboride films over the entire relevant ranges of magnetic field 0 \alt H \alt
H_{c2} (where \hcu is the upper critical field) and current density 0 \alt j
\alt j_{d} (where is the depairing current density). The intrinsic
disorder of the films combined with the large coherence length and
three-dimensionality, compared to cuprate superconductors, results in a
six-fold enhancement of and raises the depinning current density
to within an order of magnitude of . The current-voltage
response is highly non-linear at all fields, resulting from a combination of
depinning and pair-breaking, and has no trace of an Ohmic free-flux-flow
regime.
Keywords: pair, breaking, depairing, superconductor, superconductivity, flux,
fluxon, vortex, mgb