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[en] Less than two years after the discovery of high temperature superconductivity in oxypnictide LaFeAs(O, F) several families of superconductors based on Fe layers (1111, 122, 11, 111) are available. They share several characteristics with cuprate superconductors that compromise easy applications, such as the layered structure, the small coherence length and unconventional pairing. On the other hand, the Fe-based superconductors have metallic parent compounds and their electronic anisotropy is generally smaller and does not strongly depend on the level of doping, and the supposed order parameter symmetry is s-wave, thus in principle not so detrimental to current transmission across grain boundaries. From the application point of view, the main efforts are still devoted to investigate the superconducting properties, to distinguish intrinsic from extrinsic behaviors and to compare the different families in order to identify which one is the fittest for the quest for better and more practical superconductors. The 1111 family shows the highest Tc, huge but also the most anisotropic upper critical field and in-field, fan-shaped resistive transitions reminiscent of those of cuprates. On the other hand, the 122 family is much less anisotropic with sharper resistive transitions as in low temperature superconductors, but with about half the Tc of the 1111 compounds. An overview of the main superconducting properties relevant to applications will be presented. Upper critical field, electronic anisotropy parameter, and intragranular and intergranular critical current density will be discussed and compared, where possible, across the Fe-based superconductor families.
[en] This report includes data on additional superconductive materials extracted from the world literature up to fall 1977 and is an addendum to the data set published in J. Phys. Chem. Ref. Data 5, no. 3, 581-821 (1976) (Reprint no. 84). The data presented are new values and have not been selected or compared to values (except for selected values of the elements) previously assembled by the Superconductive Materials Data Center. The properties included are composition, critical temperature, critical magnetic field, crystal structure and the results of negative experiments. Special tabulations of high magnetic field materials with Type II behavior and materials with organic components are included. All entries are keyed to the literature. A list of recent reviews centered on superconductive materials is included
[en] We report our studies on the crystal structures, morphologies, and superconductivity in CeO1-xFxFeAs compounds which were fabricated by solid state reaction. The crystal structures were refined using Rietveld refinement. Superconducting properties such as critical temperature (Tc), critical current density (Jc), and upper critical field (Hc2) were determined using magneto-transport and magnetic measurement over a wide range of temperature below Tc, and in magnetic fields up to 13 T. Jc is 2 x 103 A cm-2 for the x = 0.1 sample. However, the Jc exhibited a weak dependence on magnetic field for B > 1 T and T = 5 and 10 K. A peak effect in the Jc as a function of field was observed at 20 K in the x = 0.1 sample. We estimate Hc2ab of 185 T for CeO0.9F0.1FeAs compound. The broadening of the superconducting transition near Tc with increasing field can be well understood using the thermal activated flux flow model. The pinning potential scales as U0/KB∝B-n with n = 0.2 for B < 3 T and n = 0.71 for B > 3 T in the x = 0.1 sample.
[en] Technique of critical current density measurement (Jc) of HTc bulk ceramic superconductor has been performed by using linear extrapolation with four-point probes method. The measurement of critical current density HTc bulk ceramic superconductor usually causes damage in contact resistance. In order to decrease this damage factor, we introduce extrapolation method. The extrapolating data show that the critical current density Jc for YBCO (123) and BSCCO (2212) at 77 K are 10,85(6) Amp.cm-2 and 14,46(6) Amp.cm-2, respectively. This technique is easier, simpler, and the use of the current flow is low, so it will not damage the contact resistance of the sample. We expect that the method can give a better solution for bulk superconductor application. Key words. : superconductor, critical temperature, and critical current density
[en] In this paper we present the results of critical current (I _c) measurements of MgB_2 wires made with two different set-ups of the four-point probe method: current sweep type—constant magnetic field and increasing current, and field sweep type—constant current and rapidly increasing magnetic field. Results from magnet field sweep type measurements can be interpreted by a new physical concept—a jump of the electric field in low magnetic fields. This physical concept can be correlated with damages in the Nb-barrier existing in the MgB_2 wire and be employed as a detection scheme. The damage in Nb barrier reduces critical current density (J _c) and complicates the study on critical temperature (T _c), upper critical field (B _c_2), irreversible magnetic field (B _i_r_r), pinning force (F _p), and pinning centers in superconducting MgB_2 wires. Our proposed method to detect damages in Nb barrier would benefit efforts in development and applications of MgB_2 wires. (paper)
[en] Single crystals of URu2-xRexSi2 have been grown via the Czochralski technique. Detailed electrical transport studies under pressure on single crystals of URu2Si2 confirm that the zero- temperature critical field is suppressed smoothly towards an extrapolated critical pressure of 15 kbar, which also corresponds to the accepted critical pressure of the hidden order phase. Improving on previous work on polycrystalline samples, studies of single crystals of URu2-xRexSi2 have provided more precise tracking of the suppression of both the hidden order phase at low doping and the ferromagnetic phase at intermediate Re concentrations
[en] The authors present measurements of critical currents and critical magnetic fields in cylindrical indium films. The most interesting result is that the ratio of the experimental critical current Ic1 to Silsbee's critical value Ic0 practically does not depend on temperature. This ratio was strongly dependent on the film thickness changing from Ic1 ∼0.18Ic0 for the film thickness d = 0.3 μm to Ic1 ∼ 1.3Ic0 for d = 5.5 μm. These results cannot be explained in the framework of the existing theoretical models