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Title: Vortex flux dynamics and harmonic ac magnetic response of Ba(Fe 0.94Ni 0.06) 2As 2 bulk superconductor

Vortex dynamics and nonlinear ac response are studied in a Ba(Fe 0.94Ni 0.06) 2As 2( T c= 18.5 K) bulk superconductor in magnetic fields up to 12 T via ac susceptibility measurements of the first ten harmonics. A comprehensive study of the ac magnetic susceptibility and its first ten harmonics finds shifts to higher temperatures with increasing ac measurement frequencies (10 to 10,000 Hz) for a wide range of ac (1, 5, and 10 Oe) and dc fields (0 to 12 T). The characteristic measurement time constant t1 is extracted from the exponential fit of the data and linked to vortex relaxation. The Anderson-Kim Arrhenius law is applied to determine flux activation energy E a/k as a function dc magnetic field. The de-pinning, or irreversibility lines, were determined by a variety of methods and extensively mapped. The ac response shows surprisingly weak higher harmonic components, suggesting weak nonlinear behavior. Lastly, our data does not support the Fisher model; we do not see an abrupt vortex glass to vortex liquid transition and the resistivity does not drop to zero, although it appears to approach zero exponentially.
Authors:
 [1] ; ORCiD logo [2] ; ORCiD logo [2] ;  [3] ;  [3] ;  [3]
  1. Saint Louis Univ., St. Louis, MO (United States)
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  3. Florida State Univ., Tallahassee, FL (United States)
Publication Date:
Report Number(s):
LA-UR-16-27438
Journal ID: ISSN 1557-1939; TRN: US1701769
Grant/Contract Number:
AC52-06NA25396
Type:
Accepted Manuscript
Journal Name:
Journal of Superconductivity and Novel Magnetism
Additional Journal Information:
Journal Volume: 29; Journal Issue: 11; Journal ID: ISSN 1557-1939
Publisher:
Springer
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
National Science Foundation (NSF); USDOE
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; high magnetic field science; bulk pnictides; superconductor; AC susceptibility; harmonics; irreversibility lines; activation energy; vortex dynamics; frequency shift; vortex relaxation
OSTI Identifier:
1345167