Transport and pinning properties of Ag-doped FeSe_0.94

Abstract

We investigated the superconducting transition and the pinning properties of undoped and Ag-doped FeSe 0.94 at magnetic fields up to 14 T. It was established that due to Ag addition the hexagonal phase formation in melted FeSe 0.94 samples is suppressed and the grain connectivity is strongly improved. The obtained superconducting zero-field transition becomes sharp (with a transition width below 1 K), T c and the upper critical field were found to increase, whereas the normal state resistivity significantly reduces becoming comparable with those of FeSe single crystals. In addition, a considerable magnetoresistance was observed due to Ag doping. The resistive transition of undoped and Ag-doped FeSe 0.94 is dominated by thermally activated flux flow. From the activation energy U vs H dependence, a crossover from single-vortex pinning to a collective creep pinning behavior was found with increasing the magnetic field.

Improvement of the superconducting properties of polycrystalline FeSe by silver addition

“…We demonstrated that a Kohler plot is found for the sample FeSeAg4 in the temperature interval 11K -20K [8]. However, the additional magnetoresistive measurements of this sample at higher temperatures (up to 90 K) show that the Kohler plot fails.…”

“…We established that the Ag addition in FeSe 0.94 improves both the intra-and inter-granular superconducting properties and slightly increases the irreversibility field [7]. Further investigations showed [8] that critical temperature, the magnetoresistance, the upper critical field and the activation energy for thermally activated flux flow also increased as a result of 4 wt % Ag doping. This study aims to determine the mechanism of action of silver on the superconducting properties and to optimize its content in the superconducting FeSe 0.94 .…”

“…The resistivity vs. temperature dependences ( H (T)) are investigated for all the samples at different magnetic fields up to 14 T. A moderate magnetoresistance effect (MR) is observed in samples with Ag addition (see Table 1). In the previous work [8] only one sample with 4% Ag addition was examined, so that we assumed that the registered MR (~50%) is due to Ag and Ag 2 Se impurity phases. However we established here that as the Ag addition is increased, the most intensive peak of Ag 2 Se (at 2θ=33.525) becomes a little bit stronger, while the MR is weakly suppressed (between 34% and 39% - Table 1).…”

Improved critical current densities in bulk FeSe superconductor using ball milled powders and high temperature sintering

“…Further, the J c value was increased to 1027 A cm −2 in FeSe tapes made using several‐cores of FeSe wires . Recent studies have also clarified that a small quantity of silver addition in FeSe bulk material will increase the superconducting performance as well as the flux pinning energy, respectively . In order to make reliable and reproducible bulk high performance FeSe material for several industrial applications, a further improvement of the J c is needed.…”

Effect of metal (Zn/In/Pb) additions on the microstructures and superconducting properties of Sr1−xKxFe2As2 tapes

“…Yao et al reported a large transport J c value of 1.4 × 10 4 A/cm 2 in self field and 4.2 K for the Ba 1 − x K x Fe 2 As 2 tapes with Pb and Ag co-doping where Pb addition could improve the gain connectivity and Ag addition was beneficial to grain growth [20]. It was also found that Ag addition could reduce undesired impurity phase in FeSe 0.94 [21]. Accordingly, chemical addition seems to be a very promising way to improve superconducting properties in iron pnictides.…”