Observation of weak coupling effects in Ba0.6K0.4Fe2As2junctions patterned across a naturally formed grain boundary

The magnetic behavior of an iron-based FeSe crystal sample has been studied by means of dc magnetization measurements as a function of the temperature (T), the dc magnetic field (H) and the time (t). The M(T) curves show a discrepancy in the determination of the onset of the critical temperature T C with respect to what is observed in the superconducting M(H) measurements obtained by subtracting the ferromagnetic background from the curves measured at various temperatures. By using magnetic relaxation measurements M(t), the correct value of T C has been obtained. Moreover, the superconducting M(H) loops show the presence of a noisy signal up to an anomalous 'peak effect' only found for positive and negative increasing fields. These features have been analyzed by fitting the temperature dependence of the critical current density J c (T), extracted from the M(H) loops, with the help of the J c (T) dependencies governing an S-N-S junction network. This analysis has allowed us to interpret the behavior found in the M(H) loops and to obtain the value of the intrinsic critical current density J 0 which is not influenced by the presence of the junctions.

Section: Introductionmentioning

confidence: 94%

Evaluation of the intragrain critical current density in a multidomain FeSe crystal by means of dc magnetic measurements

Galluzzi

Polichetti

Buchkov

et al. 2015

“…As it can be seen in figures 10(a)-(c), there are a lot of small grains with diameters of 0.5 μm. These small grains have weak grain connections and the superconducting current would be suppressed around them [29,30]. The 122-phase of tape 1, which is fabricated by precursor P1, has larger grains compared with tape 2, fabricated by precursor P2, and tape 3, fabricated by precursor P3.…”

Section: Resultsmentioning

confidence: 99%

Large critical current density in Cu/Ag composite sheathed (Ba,K)Fe₂As₂ tapes fabricated under ambient pressure

Yao

Dong

et al. 2019

Due to their high upper critical field (Hc2) and small anisotropy, iron-based superconductors have a great potential in high magnetic field applications. In this study, Cu/Ag composite sheathed (Ba,K)Fe2As2 (Ba-122) superconducting tapes were fabricated by an ex-situ powder-in-tube method. Moreover, an ambient pressure sintering process was adopted aiming at reducing the manufacturing cost and allowing for mass production. However, fabricating Cu/Ag composite sheathed Ba-122 tapes with a large transport Jc by an ambient pressure producing process is fairly challenging due to the absence of the over pressure. By optimizing sintering temperatures, sintering times and the composition of the raw materials, a transport Jc as high as 36 000 A cm−2 (4.2 K, 10 T) was obtained in tapes sintered at 740 °C for 3 h. The mechanism of the Jc improvement was systematically analyzed. This result is of great significance for the fabrication of low cost and long-length practical iron-based superconducting tapes.

“…Regarding applications, bicrystal experiments on K-doped Ba-122, which is believed to be an important material, should be carried out. Experiments  on single GBs in polycrystalline K-doped Ba-122 films have been reported [149]. However, the information on  well-defined, single GBs is necessary for deep understanding of GB characteristics.…”

Section: Discussion and Summarymentioning

confidence: 99%

Grain boundary characteristics of Fe-based superconductors

Iida

Hänisch

Yamamoto

2020

the distance between strained regions is smaller or only slightly larger than the value of ξ within the GB plane, the superconducting order parameter is depressed at the GB and, hence, the super-current flow is impeded. Additionally, bending of the electronic bands at GBs deplete the charge carrier density 3 , which seriously decreases the superconducting transition temperature T c . Hence, to achieve large J c for cuprates, the crystallites should not only be aligned out-of-plane because J c is anisotropic but also be aligned in-plane within the misorientation angle θ GB , where the distance between strained regions is larger than ξ ab (ξ ab : in-plane coherence length) is satisfied. On the other hand, for LTS and MgB 2 with large coherence length (e.g. 5∼6 nm) and s-wave symmetry (for MgB 2 anisotropic swave), GBs are able to pin vortices in the mixed state, and especially also GBs with rather large angles. Therefore, increasing the GB densities by reducing the grain size usually leads to improved in-field J c properties.As stated above, the symmetry of superconducting order parameter and the coherence length mainly govern the J c characteristics at GBs for a given superconductor. Hence, for both LTS and HTS, understanding the nature of GB characteristics in combination with modifying the processing conditions, so-called GB engineering, is of great importance for reducing and/or controlling the defect density to tune the superconducting properties.The Fe-based superconductors (FBS) have similar physical properties as the cuprates, for instance a short coherence length due to the small carrier concentration and a low Fermi velocity 4 . Hence, FBS also seem to share the same GB issues as the cuprates. However, J c across GBs in FBS is not as severely reduced due to several features, which is reviewed in this article. Many reviews of the synthesis of FBS in the form of bulk samples and thin films, and of their physical properties have been published to date. Additionally, excellent review articles concerning bicrystals and GBs in cuprates have already been published 3,5,6 , however, only a few on GB issues for FBS have been published (e.g. 7 and 8). Grant Number 16H04646 as well as JST CREST Grant Number JPMJCR18J4. REFERENCES 1 Tomimoto K, Terasaki I, Rykov A I, Miura T and Tajima S, 1999 Phys. Rev. B 60 114 2 Tsuei C C and Kirtley J R 2000 Rev. Mod. Phys. 72 969 3 Hilgenkamp H and Mannhart J 2002 Rev. Mod. Phys. 74 485