Journal of Low Temperature Physics

, Volume 178, Issue 5–6, pp 345–354 | Cite as

Inter- and Intra-Granular Flux Pinning Properties in Ba(Fe\(_{0.91}\)Co\(_{0.09})_{2}\)As\(_{2}\) Superconductor in AC and DC Magnetic Fields

  • M. Nikolo
  • X. Shi
  • E. S. Choi
  • J. Jiang
  • J. D. Weiss
  • E. E. Hellstrom
Article
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Abstract

Flux pinning dynamics are studied in a Ba(Fe\(_{0.91}\)Co\(_{0.09})_{2}\)As\(_{2}\) (\(T_\mathrm{{c}}=25.3\) K) bulk samples via ac susceptibility measurements. Ac susceptibility curves shift to higher temperatures as the frequency of small ac fields is increased from 75 to 1997 Hz in all magnetic fields ranging from 0 to 18 T. The temperature profile of the ac susceptibility curves shows narrower ac loss distribution in temperature for higher frequencies and gradually narrowing frequency shift as the temperature sweeps the full range from 2 K to the upper critical field temperature. The frequency (\(f)\) shift of the susceptibility curves is modeled by the Anderson–Kim Arrhenius law \(f = f_{0} \mathrm {exp}(- {E}_\mathrm{{a}} /kT)\) to determine flux activation energy \(E_\mathrm{{a}}/k\) as a function of magnetic field. Extensive mapping of the irreversibility lines shows broad dependence on the magnitude and the frequency of the ac field, in addition to the dc magnetic field. The irreversibility lines were just below the upper critical field \(H_\mathrm{{c2}}\) lines at 0 T in the \(H-T\) plane, but they moved significantly below the \(H_\mathrm{{c2}}\) line at higher magnetic fields, placing constraints on the use of these materials at higher magnetic fields such as 10 T and above.

Keywords

Superconductivity Pnictides Ac susceptibility Flux dynamics Ac losses Activation energies Magnetic measurements Upper critical field Irreversibility 
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Notes

Acknowledgments

This work at the National High Magnetic Field Laboratory was supported by NSF DMR-1006584 and DMR-1306785, the State of Florida, the U.S. Department of Energy, and by NHMFL which is supported by the National Science Foundation under DMR-1157490.

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Copyright information

© Springer Science+Business Media New York 2014

Authors and Affiliations

  • M. Nikolo
    • 1
  • X. Shi
    • 2
  • E. S. Choi
    • 2
  • J. Jiang
    • 3
  • J. D. Weiss
    • 3
  • E. E. Hellstrom
    • 3
  1. 1.Physics DepartmentSaint Louis UniversitySt. LouisUSA
  2. 2.National High Magnetic Field LaboratoryFlorida State UniversityTallahasseeUSA
  3. 3.National High Magnetic Field Laboratory, Applied Superconductivity CenterFlorida State UniversityTallahasseeUSA

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