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Title: Irreversibility Line Measurement and Vortex Dynamics in High Magnetic Fields in Ni- and Co-Doped Iron Pnictide Bulk Superconductors

The de-pinning or irreversibility lines were determined by ac susceptibility, magnetization, radio-frequency proximity detector oscillator (PDO), and resistivity methods in Ba(Fe 0.92Co 0.08) 2As 2 ( T c = 23.2 K), Ba(Fe 0.95Ni 0.05) 2As 2 ( T c = 20.4 K), and Ba(Fe 0.94Ni 0.06) 2As 2 ( T c = 18.5 K) bulk superconductors in ac, dc, and pulsed magnetic fields up to 65 T. A new method of extracting the irreversibility fields from the radio-frequency proximity detector oscillator induction technique is described. Wide temperature broadening of the irreversibility lines, for any given combination of ac and dc fields, is dependent on the time frame of measurement. Increasing the magnetic field sweep rate (dH/dt) shifts the irreversibility lines to higher temperatures up to about dH/d t = 40,000 Oe/s; for higher dH/dt, there is little impact on the irreversibility line. There is an excellent data match between the irreversibility fields obtained from magnetization hysteresis loops, PDO, and ac susceptibility measurements, but not from resistivity measurements in these materials. Lower critical field vs. temperature phase diagrams are measured. Their very low values near 0 T indicate that these materials are in mixed state in nonzero magnetic fields, and yetmore » the strength of the vortex pinning enables very high irreversibility fields, as high as 51 T at 1.5 K for the Ba(Fe 0.92Co 0.08) 2As 2 polycrystalline sample, showing a promise for liquid helium temperature applications.« less
 [1] ;  [2] ;  [2] ;  [3] ;  [3] ;  [3]
  1. Saint Louis Univ., MO (United States). Dept. of Physics
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States). National High Magnetic Field Lab. (MagLab)
  3. Florida State Univ., Tallahassee, FL (United States). National High Magnetic Field Lab. (MagLab)
Publication Date:
Report Number(s):
Journal ID: ISSN 1557-1939; TRN: US1701778
Grant/Contract Number:
AC52-06NA25396; DMR- 1006584; DMR-1306785; DMR-1157490
Accepted Manuscript
Journal Name:
Journal of Superconductivity and Novel Magnetism
Additional Journal Information:
Journal Volume: 29; Journal Issue: 11; Journal ID: ISSN 1557-1939
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE; National Science Foundation (NSF)
Country of Publication:
United States
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 36 MATERIALS SCIENCE; Superconductivity; Pnictides; Irreversibility; Magnetization; AC susceptibilityRadio frequency proximity detector oscillator
OSTI Identifier: