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Phys. Rev. B 79, 020508(R) (2009) [4 pages]

Upper and lower critical magnetic fields of superconducting NdFeAsO1−xFx single crystals studied by Hall-probe magnetization and specific heat

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Z. Pribulova1,2, T. Klein1,3, J. Kacmarcik2,4, C. Marcenat4, M. Konczykowski5, S. L. Bud’ko6, M. Tillman6, and P. C. Canfield6
1Institut Néel, CNRS, BP 166, 38042 Grenoble Cedex 9, France
2Centre of Low Temperature Physics, IEP, SAS and FS, UPJŠ, Watsonova 47, 043 53 Košice, Slovakia
3Institut Universitaire de France and Université Joseph Fourier, BP 53, 38041 Grenoble Cedex 9, France
4Institut Nanosciences et Cryogénie, SPSMS-LATEQS, CEA, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France
5Laboratoire des Solides Irradiés, Ecole Polytechnique, 91128 Palaiseau, France
6Department of Physics and Astronomy, Ames Laboratory, Iowa State University, Ames, Iowa 50011, USA

Received 15 December 2008; published 27 January 2009

The upper and lower critical fields have been deduced from specific heat and Hall-probe magnetization measurements in nonoptimally doped Nd(O,F)FeAs single crystals (Tc∼32–35 K). The anisotropy of the penetration depth (Γλ) is temperature independent and on the order of 4.0±1.5. Similarly specific-heat data lead to an anisotropy of the coherence length Γξ∼5.5±1.5 close to Tc. Our results suggest the presence of rather large thermal fluctuations and the existence of a vortex liquid phase over a broad temperature range (∼5 K large at 2 T).

© 2009 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevB.79.020508
DOI:
10.1103/PhysRevB.79.020508
PACS:
74.25.Ha, 74.25.Fy, 74.25.Nf, 74.25.Op
 
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