Biaxially textured cobalt-doped BaFe2As2 films with high critical current density over 1 MA/cm2 on MgO-buffered metal-tape flexible substrates

Abstract

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...

Anomalous scaling behavior in a mixed-state Hall effect of a cobalt-doped BaFe2As2epitaxial film with a high critical current density over 1 MA/cmSato1, Katase2, Kang3 et al. 2013Phys. Rev. BSelf Cite17170View full textAdd to dashboardCite

“…1 clearly, exist in BaFe 2 As 2 :Co epitaxial film. [19] The F p maximum position of BaFe 2 As 2 :Co epitaxial film is about 0.4 H/H irr [16] , indicating that origin of the pinning is not purely the collective pinning and includes the strong core pining. This mechanism is similar to the case of columnar BaFeO 2 pinning centers [47] in a BaFe 2 As 2 :Co epitaxial film grown using SrTiO 3 buffer layer.…”

“…However, their superior grain boundary properties [10] along with high upper critical magnetic fields (H c2 ) ≥ 50 T and small anisotropic factors γ = H c2 //ab / H c2 //c = 1-2 [11] are promising for wire [12][13][14] and tape applications. [15,16] Similar to cuprates, the extrinsic pinning centers largely control J c in iron pnictides. Therefore, the vortex pinning mechanism for high-J c BaFe 2 As 2 :Co epitaxial films is important to understand the ultimate potential of the iron pnictide superconducting wires and tapes.…”

High transport critical current densities in textured Fe-sheathed Sr1−xKxFe2As2+Sn superconducting tapes

“…These results suggest that the discovered iron based superconductors are exhibiting weak link grain boundary behavior similar to high-T c cuprate superconductors. An effective method to overcome the weak link problem is to engineering textured grains in iron based superconductors to minimize deterioration of the critical current density across high-angle grain boundaries.Recently Co-doped Ba122 coated conductors have been grown by several groups utilizing the existing YBCO coated conductor technology and have reached a self-field J c over 1 MA/cm 2 [21][22][23]. However, the technology has the shortcoming of low production rate, complexity and high equipment cost.…”

“…Recently Co-doped Ba122 coated conductors have been grown by several groups utilizing the existing YBCO coated conductor technology and have reached a self-field J c over 1 MA/cm 2 [21][22][23]. However, the technology has the shortcoming of low production rate, complexity and high equipment cost.…”

Critical factor for epitaxial growth of cobalt-doped BaFe2As2 films by pulsed laser deposition

“…[2][3][4][5][6][7] These materials are advantageous for high magnetic-field applications, such as superconducting wires and tapes, because they have high upper critical fields of >50 T, 8 small anisotropy factors, 9 and good grain boundaries. 10 Many researchers have reported superconducting wires [11][12][13] and tapes [14][15][16] made from these materials that exhibit high critical current densities (J c ) under high magnetic fields.…”