The changes in the superconducting properties of high-temperature superconducting tapes of the second generation within a wide range of temperatures and applied magnetic fields up to 7 T before and ...after irradiation with gold and nickel ions were studied using the vibrational magnetometer technique. We assume the experimental results obtained to be related to a different mechanism of vortex structure pinning in the samples.
Data on magnetization, magnetic susceptibility and microstructure modification of irradiated Nb3Sn platelets are presented. The irradiation was produced at room temperature by fast protons with the ...energies of 12.4 and 12.8 MeV with fluencies of 5x1017 and 1x1018 cm-2. Variation of the superconducting transition temperature versus irradiation dose was determined. Temperature dependence of magnetic susceptibility of Nb3Sn platelet with 160 μm thickness demonstrates several steps corresponding to different superconducting transition temperatures. We supposed that there are layers inside the sample with significantly different radiation damage levels caused by particles movement termination (Bragg peak). It was found that after the irradiation a lot of randomly oriented platelet-like Nb-enriched particles of 0.1-0.5 μm size appear in volumes with maximal damages.
We present our results on utilization of the quantum levitation effect for HTSC samples (superconducting ceramics based on YBa
2
Cu
3
O
7
−x
and SuperOx J-PI-12-20Ag-20Cu superconducting tapes) in ...magnetic fields of different configurations with respect to developing special carriers for hybrid systems of noncontact transport of cryogenic targets in ICF experiments. We implement the obtained results for developing and engineering of “HTSC-MAGLEV” delivery system to minimize the risk for damage of the fuel layer at the target acceleration and during target injection into the center of the ICF reaction chamber.
The pinning force,
F
p
, is studied in Nb films of different thickness in parallel magnetic field
H
. The asymmetry in the magnetic field dependence of
F
p
has been observed for two opposite ...directions of the transport current. The effect is less pronounced for thin and thick films where, respectively, single vortex pinning and pinning of the internal vortices, is relevant. At intermediate thickness, where the pinning mechanism is mostly caused by surface effects, an asymmetry in the
F
p
(
H
) dependence is clearly visible. The different surface barriers that vortices should overcome to enter the sample from opposite sides of the film explain the effect, as confirmed by numerical calculations. These have been obtained by solving the Ginzburg–Landau equations with asymmetric boundary conditions which take into account the different superconducting properties of the film–substrate and film–vacuum interface. Such difference can also explain the reduction of the critical current usually observed in thin films as a function of their thickness.
The behavior of a superconducting plate with transport current in a magnetic field parallel to its surface was studied by using numerical solution of Ginzburg-Landau (GL) equations. Boundary ...conditions for the order parameter in their general form have been used. The boundary conditions allow to consider the influence of the plate's boundaries on the superconducting state inside it. According to the calculations some features of the dependences of critical current and critical magnetic field in the parallel to the plate's surface direction as a function of the plate thickness have been detected. Such dependences are not explained by standard formulas for thin plates. On the basis of the calculations, an approach to estimate the coherence length ξ has been proposed. The results of the calculations are consistent with experimental data and qualitative analysis of the calculations within GL theory.
Temperature dependences of resistivity, magnetic susceptibility, and charge-carrier concentration and mobility in single-crystalline PbTe:V samples with a varied impurity content are investigated. It ...is shown that vanadium forms a donor level located ∼20 meV below the conduction-band bottom. The electron mobility is as high as 10
5
cm
2
V
−1
s
−1
in the samples with
N
V
≤ 0.21 at % and proves to be more than an order of magnitude higher in the samples with the highest vanadium content
N
V
= 0.26 at %. In the same samples, the real part of the conductivity is characterized by a pronounced frequency dependence. An increase in vanadium concentration is accompanied by a decrease in the effective magnetic moment of impurity atoms. The features of electron transport in PbTe:V may be caused by a variable vanadium valence and by the effect of interimpurity correlations.
We have grown and characterized three samples of Co doped MnSi and studied their physical properties (magnetization and magnetic susceptibility, heat capacity and electrical resistance). All three ...samples show non-Fermi liquid physical properties. From literature data and current results follow that impurities (Co and Fe) eliminate the first order phase transition peaks and spread the fluctuation maxima in such a way that its low temperature part effectively reaches the zero temperature, where the fluctuations inevitably become quantum. The behavior of low temperature branches of the heat capacity of the samples suggests that a gradual transition from classical to quantum fluctuations can be described by a simple power function of temperature with the exponent less than one. The \(d\rho/dT\) data generally support this suggestion. The values of the heat capacity exponents immediately lead to the diverging ratio \(C_p/T\) and hence to the diverging effective electron mass. We found out that at large concentration of the dopant there are no distinct phase transition points. What we observe is a cloud of the helical fluctuations spreading over a significant range of concentrations and temperatures, which become quantum close to 0~K.
We report on successful fabrication of superconducting FeSe wire using hot gas extrusion (HGE) ex-situ PIT (powder in tube) method. Length of the obtained wire was about 60cm with cross-sectional ...superconducting core area nearly 2.5 × 10−3 cm2. For the wire sample we observed superconducting transition temperature, Tonsetc ≈ 11 K, about 1.2K lower compared to preliminary prepared FeSe powder. Heat treatment in argon atmosphere at 350oC resulted in transition width decrease from ΔT(10% − 90%) ≈ 1.75 K in sample without heat treatment down to ΔT ≈ 0.9 K in annealed samples. Estimated derivative of the upper critical field as a function of temperature of the sample annealed during 72h in argon atmosphere at 350oC is dHc2/dT ∼ −2.9 T/K. Applying WHH theory to our data allows to define Hc2(0K) 0.69Tc × (dHc2/dT) ≈ 19.8T. The untreated wire shows critical current density, Jc ∼ 75 A/cm2 at T=4.0 K in zero field. Increasing annealing time up to 72 hours at 350oC in argon atmosphere gives rise to Jc increase of about 60% approaching 120 A/cm2 at T=4.0K and H=0T . Also Jc measurements were made in magnetic fields up to 9T. Our results show applicability of the HGE PIT method for fabrication of superconducting wires based on FeSe compound. Long-range heat treatment is necessary to improve superconducting properties of the samples.
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