High critical current densities (J c ) > 1 MA/cm 2 were realized in cobalt-doped BaFe 2 As 2 (BaFe 2 As 2 :Co) films on flexible metal substrates with biaxially-textured MgO base-layers fabricated by an ion-beam assisted deposition technique. The BaFe 2 As 2 :Co films showed small in-plane crystalline misorientations ( BaFe2As2:Co ) of ~3 o regardless of twice larger misorientaions of the MgO base-layers ( MgO = 7.3 o ), and exhibited high self-field J c up to 3.5 MA/cm 2 at 2 K. These values are comparable to that on MgO single crystals and the highest J c among iron pnictide superconducting tapes and wires ever reported. High in-field J c suggests the existence of c-axis correlated vortex pinning centers. --------------------------------------------------------Footnotes:(*) Electronic mail: hosono@msl.titech.ac.jp J c (H//c) curves monotonically decrease with increasing H, but the slopes (dJ c /dH) for Film/IBAD are smaller than those for Film/sc-MgO, which would originate from a stronger vortex pinning effect along the c-axis and also from the higher T c with high irreversibility field of the Film/IBAD. Figure 3 (b) shows the J c (H//ab) and J c (H//c) dependences at 4-18 K for Film/IBAD with  MgO = 6.1 o . J c (H//ab) is larger than J c (H//c) in almost the whole H range at 4 K, while crossovers are observed at 5.0 T at 12 K and 2.9 T at 16 K, respectively. At a higher T of 18 K, J c (H//c) is greater than J c (H//ab) in the whole H region. These results are different from the J c (H) curves for T. Katase et al. 8 BaFe 2 As 2 :Co single crystals, which show the relation of J c (H//ab) > J c (H//c) in the whole H and T region 29 that is reasonable based on the intrinsic anisotropy of H c2 (i.e.;H c2 //ab > H c2 //c) 6 . These results suggest the existence of strong vortex pinning centers along the c-axis in Film/IBAD, which is effective at high T ≥ 12 K in the low H region less than several T. The inset figure plots the pinning force density F p = J c × 0 H as a function of H measured in H//c at T = 4-18 K. Each F p curve takes a peak (F pmax ) as indicated by arrows in the inset at T ≥ 12 K. The largest F pmax is ~8 GN/m 3 at 4 K but is three times smaller than those of BaFe 2 As 2 :Co epitaxial films on LSAT single crystals (30 GN/m 3 at ~12 T) 30 . It suggests that much higher in-field J c would be realized on IBAD substrates by further optimizing the c-axis correlated pinning centers.In conclusion, we demonstrated high self-field J c = 1.2-3.6 MA/cm 2 at 2 K for BaFe 2 As 2 :Co films directly grown on IBAD-MgO buffered flexible metal substrates.The biaxially-textured BaFe 2 As 2 :Co films exhibited excellent in-plane alignment with  BaFe2As2:Co ~3 o regardless of the larger  MgO = 5.5-7.3 o of the MgO base-layers. The in-field J c of the BaFe 2 As 2 :Co films on the IBAD substrates is substantially higher than that for BaFe 2 As 2 :Co films on MgO single crystals, probably due to c-axis vortex pinning effects. These results imply that high J c coated conductors can be fabricated with BaFe 2 As 2...

The high upper critical field characteristic of the recently discovered iron-based superconducting chalcogenides opens the possibility of developing a new type of non-oxide high-field superconducting wires. In this work, we utilize a buffered metal template on which we grow a textured FeSe 0.5 Te 0.5 layer, an approach developed originally for high temperature superconducting coated conductors. These tapes carry high critical current densities (>1×10 4 A/cm 2 ) at about 4.2 K under magnetic field as high as 25 T, which are nearly isotropic to the field direction. This demonstrates a very promising future for iron chalcogenides for high field applications at liquid helium temperatures. Flux pinning force analysis indicates a point defect pinning mechanism, creating prospects for a straightforward approach to conductor optimization.

The biaxially textured growth of superconducting Co-doped BaFe2As2 (Ba-122) thin films has been realized on ion beam assisted deposition (IBAD) MgO coated conductor templates by employing an iron buffer architecture. The iron pnictide coated conductor showed a superconducting transition temperature of 21.5 K, which is slightly lower than that of Co-doped Ba-122 films on single crystalline MgO substrates. A self-field critical current density of over 10 5 A·cm −2 has already been achieved even at 8 K. The current experiment highlights the potential of possible coated conductor applications of the iron-based superconductors.

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Optimized, biaxially textured BaFe1.8Co0.2As2 thin films with an in-plane alignment of 1.7° have been realized on high-quality IBAD-textured MgO-coated technical substrates utilizing additional Fe buffer layers. High critical current densities (Jc) were achieved, comparable to films on single crystalline MgO (Jc ≥ 1 MA cm−2 at 4 K, self-field). Transmission electron microscopy investigations reveal a small number of c-axis correlated defects introduced by the MgO template. The effect of these defects on the Jc anisotropy was determined in angular-dependent electronic transport measurements.