Small anisotropy, weak thermal fluctuations, and high field superconductivity in Co-doped iron pnictide Ba (Fe1-xCox) 2As2

A. Yamamoto, J. Jaroszynski, C. Tarantini, L. Balicas, J. Jiang, A. Gurevich, D. C. Larbalestier, R. Jin, A. S. Sefat, M. A. McGuire, B. C. Sales, D. K. Christen, D. Mandrus

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Abstract

We performed high-field magnetotransport and magnetization measurements on a single crystal of the 122-phase iron pnictide Ba (Fe1-xCo x) 2As2. Unlike the high-temperature superconductor cuprates and 1111-phase oxypnictides, Ba (Fe1-xCo x) 2As2 showed practically no broadening of the resistive transitions under magnetic fields up to 45 T. We report the temperature dependencies of the upper critical field Hc2 both parallel and perpendicular to the c -axis, the irreversibility field H irr c (T), and a rather unusual symmetric volume pinning force curve Fp (H) suggestive of a strong pinning nanostructure. The anisotropy parameter γ= Hc2ab/ Hc2c deduced from the slopes of d Hc2ab /dT=4.9 T/K and d Hc2 c /dT=2.5 T/K decreases from ∼2 near T c, to ∼1.5 at lower temperatures, much smaller than γ for 1111pnictides and high- Tc cuprates.

Original languageEnglish
Article number062511
JournalApplied Physics Letters
Volume94
Issue number6
DOIs
StatePublished - 2009

Funding

Work at the NHMFL was supported by the NSF Cooperative Agreement DMR-0084173, by the State of Florida, by the DOE and by AFOSR under Grant No. FA9550-06-1-0474. Work at ORNL was supported by the Division of Materials Science and Engineering, Office of Basic Energy Sciences. AY is supported by a fellowship of the JSPS.

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