Vortex pinning in artificially layered Ba(Fe,Co)2As2 film

Abstract Static high critical current densities ( J c ) > 1 MA/cm 2 with magnetic field parallel or perpendicular to c -axis were realized in Co-doped/undoped multilayerd BaFe 2 As 2 films. We made a current bridge by FIB to allow precise measurements, and confirmed that the boundary quality using FIB was considerably better than the quality achieved using a laser. The presence of a high in-plane J c suggested the existence of c -axis correlated vortex pinning centers. To clarify the relationship between the J c performance and superstructures, we investigated the magnetic flux pinning mechanism using scaling theory of the volume pinning force F p ( H ). The J c ( H ) curves, F p / F p,max vs. h =  H / H irr curves, and parameters p and q depended on the characteristics of the flux pinning mechanism. It was found that the dominant pinning mechanism of Co-doped/undoped multilayerd BaFe 2 As 2 films was Δl-pinning and the inserted undoped BaFe 2 As 2 layers remained non-superconducting. The dominant pin geometry varied when the magnetic field direction changed. It was concluded that the artificially layered BaFe 2 As 2 film is a 3-D superconductor due to its long correlation length compared to the thickness of the non-superconducting layer.

[1]  Sun,et al.  Vortex confinement by columnar defects in YBa2Cu3O7 crystals: Enhanced pinning at high fields and temperatures. , 1991, Physical review letters.

[2]  W. Kwok,et al.  Enhancement of the critical current density by increasing the collective pinning energy in heavy ion irradiated Co-doped BaFe2As2 single crystals , 2015 .

[3]  D. Song,et al.  Doping-dependent critical current properties in K, Co, and P-doped BaF e 2 A s 2 single crystals , 2017, 1701.01578.

[4]  David J. Singh,et al.  Superconductivity at 22 K in Co-doped BaFe2As2 crystals. , 2008, Physical review letters.

[5]  K. Tanabe,et al.  Influence of random point defects introduced by proton irradiation on critical current density and vortex dynamics of Ba(Fe0.925Co0.075)2As2 single crystals , 2012 .

[6]  Fisher,et al.  Vortex-glass superconductivity: A possible new phase in bulk high-Tc oxides. , 1989, Physical review letters.

[7]  Y. Nakajima,et al.  Enhancement of critical current density and vortex activation energy in proton-irradiated Co-doped BaFe 2 As 2 , 2012, 1209.3281.

[8]  D. Christen,et al.  Small anisotropy, weak thermal fluctuations, and high field superconductivity in Co-doped iron pnictide Ba(Fe1-xCox)2As2 , 2008, 0810.0699.

[9]  Y. Nakajima,et al.  Enhancement of Critical Current Densities in Co-Doped BaFe$_{2}$As$_{2}$ with Columnar Defects Introduced by Heavy-Ion Irradiation , 2009, 0906.0444.

[10]  Jiaqiang Yan,et al.  Vortex phase diagram of Ba(Fe 0.93 Co 0.07 ) 2 As 2 single crystals , 2008, 0810.1338.

[11]  Maw-Kuen Wu,et al.  A semi-quantitative method to analyze the complex pinning mechanisms in single-grained high-T/sub c/ superconductors , 2005 .

[12]  S. Dou,et al.  Hydrostatic pressure induced transition from δTC to δℓ pinning mechanism in MgB2 , 2014, 1412.4860.

[13]  C. M. Folkman,et al.  Artificial and self-assembled vortex-pinning centers in superconducting Ba(Fe 1 − x Co x ) 2 As 2 thin films as a route to obtaining very high critical-current densities , 2012 .

[14]  Gallagher,et al.  Experimental evidence for vortex-glass superconductivity in Y-Ba-Cu-O. , 1989, Physical review letters.

[15]  F. Balakirev,et al.  Nearly isotropic superconductivity in (Ba,K)Fe2As2 , 2008, Nature.

[16]  Very High Field Two-Band Superconductivity in LaFeAsO_0.89F_0.11 , 2008, 0804.0485.

[17]  P. Schätzle,et al.  Enhanced flux pinning in (Nd0.33Sm0.67)Ba2Cu3O7−δ melt-processed superconductors by Ar postannealing , 1999 .

[18]  S. Dou,et al.  Effect of sample size on magnetic Jc for MgB2 superconductor , 2003, cond-mat/0304004.

[19]  Nakayama,et al.  High Critical-Current Density in the Heavily Pb-Doped Bi2Sr2CaCu2O8+delta Superconductor: Generation of Efficient Pinning Centers , 1997, Science.

[20]  P. Mele,et al.  Artificial pinning center technology to enhance vortex pinning in YBCO coated conductors , 2009 .

[21]  Q. X. Jia,et al.  Strongly enhanced current densities in superconducting coated conductors of YBa2Cu3O7–x + BaZrO3 , 2004, Nature materials.

[22]  L. Schultz,et al.  Oxypnictide SmFeAs(O,F) superconductor: a candidate for high–field magnet applications , 2013, Scientific Reports.

[23]  V. Selvamanickam,et al.  The low-temperature, high-magnetic-field critical current characteristics of Zr-added (Gd,Y)Ba2Cu3Ox superconducting tapes , 2012 .

[24]  Sanghan Lee,et al.  High critical current density over 1 MA cm−2 at 13 T in BaZrO3 incorporated Ba(Fe,Co)2As2 thin film , 2017 .

[25]  B. Buchner,et al.  Critical current and vortex dynamics in single crystals of Ca(Fe 1-x Co x ) 2 As 2 , 2010, 1004.3910.

[26]  A. Malagoli,et al.  Application potential of Fe-based superconductors , 2015 .

[27]  Shoji Tanaka,et al.  A new type of pinning center in melt grown Nd123 and Sm123 , 1994 .

[28]  D. Dew-Hughes.  Flux pinning mechanisms in type II superconductors , 1974 .