21 research outputs found
Superconductivity at 36 K in Gadolinium-arsenide Oxides GdOFFeAs
In this paper we report the fabrication and superconducting properties of
GdOFFeAs. It is found that when x is equal to 0.17,
GdOFFeAs is a superconductor with the onset transition
temperature T 36.6K. Resistivity anomaly near 130K was
observed for all samples up to x = 0.17, such a phenomenon is similar to that
of LaOFFeAs. Hall coefficient indicates that
GdOFFeAs is conducted by electron-like charge carriers.Comment: 3 pages, 4 figure
Vortex creep and critical current densities in superconducting (Ba,K)FeAs single crystals
The surprisingly rapid relaxation of the sustainable current density in the
critical state of single crystalline BaKFeAs is
investigated for magnetic fields oriented parallel to the c-axis and to the
--plane respectively. Due to the inadequacy of standard analysis procedures
developed for flux creep in the high temperature superconducting cuprates, we
develop a simple, straightforward data treatment technique that reveals the
creep mechanism and the creep exponent . At low magnetic fields, below the
second magnetization peak, varies only slightly as function of
temperature and magnetic flux density . From the data, we determine the
temperature- and field dependence of the effective activation barrier for
creep. At low temperatures, the measured current density approaches the
zero--temperature critical current density (in the absence of creep) to within
a factor 2, thus lending credence to earlier conclusions drawn with respect to
the pinning mechanism. The comparable values of the experimental screening
current density and the zero-temperature critical current density reveals the
limited usefulness of the widely used "interpolation formula".Comment: Physical Review B (2012) Accepte
Superconductivity in Ti-doped Iron-Arsenide Compound Sr4Cr0.8Ti1.2O6Fe2As2
Superconductivity was achieved in Ti-doped iron-arsenide compound
Sr4Cr0.8Ti1.2O6Fe2As2 (abbreviated as Cr-FeAs-42622). The x-ray diffraction
measurement shows that this material has a layered structure with the space
group of \emph{P4/nmm}, and with the lattice constants a = b = 3.9003 A and c =
15.8376 A. Clear diamagnetic signals in ac susceptibility data and
zero-resistance in resistivity data were detected at about 6 K, confirming the
occurrence of bulk superconductivity. Meanwhile we observed a superconducting
transition in the resistive data with the onset transition temperature at 29.2
K, which may be induced by the nonuniform distribution of the Cr/Ti content in
the FeAs-42622 phase, or due to some other minority phase.Comment: 3 pages, 3 figure
Determination of incommensurate modulated structure in Bi2Sr1.6La0.4CuO6+{\delta} by aberration-corrected transmission electron microscopy
Incommensurate modulated structure (IMS) in Bi2Sr1.6La0.4CuO6+{\delta}
(BSLCO) has been studied by aberration corrected transmission electron
microscopy in combination with high-dimensional (HD) space description. Two
images in the negative Cs imaging (NCSI) and passive Cs imaging (PCSI) modes
were deconvoluted, respectively. Similar results as to IMS have been obtained
from two corresponding projected potential maps (PPMs), but meanwhile the size
of dots representing atoms in the NCSI PPM is found to be smaller than that in
PCSI one. Considering that size is one of influencing factors of precision,
modulation functions for all unoverlapped atoms in BSLCO were determined based
on the PPM obtained from the NCSI image in combination with HD space
description
Effect of nano-C doping on the in-situ processed MgB2 tapes
The effect of nano-C doping on the microstructure and superconducting
properties of Fe-sheathed MgB2 tapes prepared through the in-situ
powder-in-tube method was studied. Heat treatment was performed at a low
temperature of 650C for 1 h. Scanning electron microscopy investigation
revealed that the smaller grain size of MgB2 in the samples with the C-doping.
Further, the a-axis lattice parameter and transition temperature decreased
monotonically with increasing doping level, which is due to the C substitution
for B. High critical current density Jc values in magnetic fields were achieved
in the doped samples because of the very fine-grained microstructure of the
superconducting phase obtained with C doping.Comment: revised manuscript, 4 pages, 4 figures. to be published soo
Multi-Band Exotic Superconductivity in the New Superconductor Bi4O4S3
Resistivity, Hall effect and magnetization have been investigated on the new
superconductor Bi4O4S3. A weak insulating behavior has been induced in the
normal state when the superconductivity is suppressed. Hall effect measurements
illustrate clearly a multiband feature dominated by electron charge carriers,
which is further supported by the magnetoresistance data. Interestingly, a kink
appears on the temperature dependence of resistivity at about 4 K at all high
magnetic fields when the bulk superconductivity is completely suppressed. This
kink can be well traced back to the upper critical field Hc2(T) in the low
field region, and is explained as the possible evidence of residual Cooper
pairs on the one dimensional chains.Comment: 5 pages, 5 figure
Superconducting properties of SmO1-xFxFeAs wires with Tc = 52 K prepared by the powder-in-tube method
We demonstrate that Ta sheathed SmO1-xFxFeAs wires were successfully
fabricated by the powder-in-tube (PIT) method for the first time. Structural
analysis by mean of x-ray diffraction shows that the main phase of SmO1-xFxFeAs
was obtained by this synthesis method. The transition temperature of the
SmO0.65F0.35FeAs wires was confirmed to be as high as 52 K. Based on
magnetization measurements, it is found that a globe current can flow on
macroscopic sample dimensions with Jc of ~3.9x10^3 A/cm^2 at 5 K and self
field, while a high Jc about 2x10^5 A/cm^2 is observed within the grains,
suggesting that a significant improvement in the globle Jc is possible. It
should be noted that the Jc exhibits a very weak field dependence behavior.
Furthermore, the upper critical fields (Hc2) determined according to the
Werthamer-Helfand-Hohenberg formula are (T= 0 K) = 120 T, indicating a very
encouraging application of the new superconductors.Comment: 14 pages, 6 figure
Observation of quantum effects of vortices in MgB2 superconductors
Irreversibility lines and magnetic relaxation of MgB2 are studied. The large separation between irreversibility line and upper critical magnetic field for T → 0 is explained by quantum fluctuations of vortices. Theoretical fits are in good agreement with experimental data. Magnetic relaxation rates of MgB2 are studied. A quantum correction of the relaxation rate is proposed, leading to a simple evaluation of the energy barrier: U0(T,H) ∼ Uth(T)UH(H) ∝ (1 - T/Tc)α(μ0H)β with α ∼ 1.5 and β ∼ -2.0. © 2003 Elsevier Science B.V. All rights reserved.SCOPUS: cp.jinfo:eu-repo/semantics/publishe