191 research outputs found
Anisotropic AC Behavior of Multifilamentary Bi-2223/Ag Tapes
In this communication, we report on the anisotropy of the superconducting
properties of multifilamentary Bi-based tapes experimentally investigated by AC
magnetic susceptibility measurements. The susceptibility was measured using a commercial system and a couple of orthogonal
pick-up coils. The vs. temperature curves were shown to exhibit two
peaks. The smaller of the peaks, occurring near T = 72K, was only visible for
particular field directions and within a given frequency window. Such results
point out the role played by the phase difference between the applied magnetic
field and the internal magnetic field seen by the filaments.Comment: 4 pages (2 columns); 4 figure
From RE-211 to RE-123. How to control the final microstructure of superconducting single-domains
This paper reviews the usual techniques for producing YBCO-type
single-domains and the microstructure of the as-obtained samples. The problems
of seed dissolution and parasite nucleations are discussed in details.
Formation of microstructural defects, such as pores and cracks, are examined.
An important part of this review is devoted to the study of the influence of
RE-211 particles [RE2BaCuO5 where RE denotes Y, Yb, Nd, Sm, Dy, Gd, Eu or a
mixture of them. Generally Nd4Ba2Cu2O10 is preferred to Nd2BaCuO5] on the
microstructure and properties of RE-Ba-Cu-O single-domains. Trapping/Pushing
theory is described in order to explain the spatial distribution of RE-211
particles in the RE-123 [(RE)Ba2Cu3O7-d] monoliths. Formation of RE-211-free
regions is discussed. Different ways to limit the RE-211 coarsening are
reviewed. Microstructural defects in the RE-123 matrix caused by the RE-211
particles are presented. It is also shown that RE-211 particles play a
significant role on the mechanical properties of single-domain samples. We
finish this review by discussing the Infiltration and Growth process as a good
technique to control the microstructure.Comment: review paper to be published in Supercond. Sci. Technol.; 19 figures;
137 references; 37 page
Magnon-polaron and Spin-polaron Signatures in the Specific Heat and Electrical Resistivity of in Zero Magnetic Field, and the Effect of Bond Environment
, an perovskite manganite oxide,
exhibits a non trivial behavior in the vicinity of the sharp peak found in the
resistivity as a function of temperature in zero magnetic field. The
various features seen on are discussed in terms of competing phase
transitions. They are related to the bond environment depending on
the content of the crystallographic site. A Ginzburg-Landau type theory is
presented for incorporating concurrent phase transitions. The specific heat
of such a compound is also examined from 50 till 200 K. A log-log analysis
indicates different regimes. In the low temperature conducting ferromagnetic
phase, a collective magnon signature () is found as for what
are called magnon-polaron excitations. A law is found at
high temperature and discussed in terms of the fractal dimension of the
conducting network of the weakly conducting (so-called insulating) phase and
Orbach estimate of the excitation spectral behaviors. The need of considering
both independent spin scattering and collective spin scattering is thus
emphasized. The report indicates a remarkable agreement for the Fisher-Langer
formula, i.e. at second order phase transitions. Within
the Attfield model, we find an inverse square root relationship between the
critical temperature(s) and the total local strain.Comment: 19 pages, 5 figures; to be published in Phys Rev
Magneto - transport characterization of Dy123 monodomain superconductors
The following report considers textured materials of the DyBa2Cu3O7 type
seeded with a Nd123 seed as initiator. They are grown with an excess 20% Dy211
phase on a Dy2O3 substrate. We report chemical characterizations, electrical
resistivity, thermoelectric power and thermal conductivity over a broad
temperature range as a function of an applied magnetic field up to 6 T. We show
that specific features appear on the magneto thermal transport properties
different in these materials from those found in single crystals and
polycrystalline samples. We propose that two vortex regimes can be
distinguished in the mixed phase, - due to the intrinsic microstructure. We
calculate the viscosity, entropy and figure of merit of the samples.Comment: 18 pages, with 8 figures; 4 color figuresx missing (much memory
needed
Microwave properties of DyBa_2Cu_3O_(7-x) monodomains and related compounds in magnetic fields
We present a microwave characterization of a DyBaCuO
single domain, grown by the top-seeded melt-textured technique. We report the
(a,b) plane field-induced surface resistance, , at 48.3 GHz,
measured by means of a cylindrical metal cavity in the end-wall-replacement
configuration. Changes in the cavity quality factor Q against the applied
magnetic field yield at fixed temperatures. The temperature
range [70 K ; T_c] was explored. The magnetic field 0.8 T was
applied along the c axis. The field dependence of does not
exhibit the steep, step-like increase at low fields typical of weak-links. This
result indicates the single-domain character of the sample under investigation.
exhibits a nearly square-root dependence on H, as expected for
fluxon motion. From the analysis of the data in terms of motion of Abrikosov
vortices we estimate the temperature dependences of the London penetration
depth and the vortex viscosity , and their zero-temperature
values 165 nm and 3 10 Nsm, which are
found in excellent agreement with reported data in YBaCuO
single crystals. Comparison of microwave properties with those of related
samples indicate the need for reporting data as a function of T/T_c in order to
obtain universal laws.Comment: 6 pages, 4 figures, LaTeX, submitted to Journal of Applied Physic
The contribution of 211 particles to the mechanical reinforcement mechanism of 123 superconducting single domains
Hardness and fracture toughness of Dy-123 single-domains were studied by
Vickers micro-indentation. A significant anisotropy of the mechanical
properties was observed. Hardness tests give higher values when performed in
(001) planes rather than in planes parallel to the c-axis. Moreover cracks
pattern around the indentation follows preferential orientation in planes
parallel to the c-axis whereas a classical ''four-cracks'' pattern is observed
in the (001) planes. It has been possible to show the crucial role played by
the 211-particles in the deviating mechanism of cracks and the relevance of the
211-particle distribution high homogeneity in the material.Comment: 14 pages, including 5 figures and 1 Table. submitted to Supercond.
Sci. Techno
Magneto-transport study of nb-doped Bi/Pb2223 superconductor
The magneto-transport properties of Bi1.5Pb0.4Nb0.1Sr2Ca2Cu3O10-x polycrystalline, superconducting ceramic are reported. The material was found to be chemically homogeneous and partially textured. The mixed state properties were investigated by measuring the electrical resistivity, longitudinal and transverse (Nernst effect) thermoelectric power, and thermal conductivity. The magnetization and AC susceptibility measurements were also performed. The variation of these characteristics for magnetic fields up to 5 T are discussed and compared to those of the zero field case. The transport entropy and thermal Hall angle are extracted and quantitatively compared to previously reported data of closely related systems. (C) 2003 Elsevier Science B.V. All rights reserved
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