Effects of Co substitution on thermodynamic and transport properties and anisotropic Hc2 in Ba(Fe1xCox)2As2 single crystals

N. Ni, M. E. Tillman, J.-Q. Yan, A. Kracher, S. T. Hannahs, S. L. Bud’ko, and P. C. Canfield
Phys. Rev. B 78, 214515 – Published 29 December 2008

Abstract

Single crystalline samples of Ba(Fe1xCox)2As2 with x<0.12 have been grown and characterized via microscopic, thermodynamic, and transport measurements. With increasing Co substitution, the thermodynamic and transport signatures of the structural (high-temperature tetragonal to low-temperature orthorhombic) and magnetic (high-temperature nonmagnetic to low-temperature antiferromagnetic) transitions are suppressed at a rate of roughly 15 K/% Co. In addition, for x0.038 superconductivity is stabilized, rising to a maximum Tc of approximately 23 K for x0.07 and decreasing for higher x values. The Tx phase diagram for Ba(Fe1xCox)2As2 indicates that either superconductivity can exist in both low-temperature crystallographic phases or that there is a structural phase separation. Anisotropic superconducting upper critical-field data [Hc2(T)] show a significant and clear change in anisotropy between samples that have higher temperature structural phase transitions and those that do not. These data show that the superconductivity is sensitive to the suppression of the higher temperature phase transition.

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  • Received 11 November 2008

DOI:https://doi.org/10.1103/PhysRevB.78.214515

©2008 American Physical Society

Authors & Affiliations

N. Ni1, M. E. Tillman1, J.-Q. Yan1, A. Kracher1, S. T. Hannahs2, S. L. Bud’ko1, and P. C. Canfield1

  • 1Ames Laboratory U.S. DOE and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
  • 2National High Magnetic Field Laboratory, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310, USA

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Issue

Vol. 78, Iss. 21 — 1 December 2008

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