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Upper critical magnetic field in Ba(0.68)K(0.32)Fe(2)As(2) and Ba(Fe(0.93)Co(0.07))(2)As(2)

TitleUpper critical magnetic field in Ba(0.68)K(0.32)Fe(2)As(2) and Ba(Fe(0.93)Co(0.07))(2)As(2)
Publication TypeJournal Article
Year of Publication2011
AuthorsGasparov VA, Drigo L, Audouard A, Sun DL, Lin CT, Bud'ko SL, Canfield PC, Fabris FW, Wosnitza J
Journal TitleJETP Letters
Volume93
Pages667-672
Date Published08
Type of ArticleArticle
ISBN Number0021-3640
Accession NumberWOS:000293477100010
Keywordssuperconductors
Abstract

We report measurements of the temperature dependence of the radio frequency magnetic penetration depth in Ba(0.68)K(0.32)Fe(2)As(2) and Ba(Fe(0.93)Co(0.07))(2)As(2) single crystals in pulsed magnetic fields up to 60 T. From our data, we construct an H-T-phase diagram for the inter-plane (H aEuro- c) and in-plane (H aEuro- ab) directions for both compounds. For both field orientations in Ba(0.68)K(0.32)Fe(2)As(2) we find a concave curvature of the H (c2)(T) lines with decreasing anisotropy and saturation towards lower temperature. Taking into account Pauli spin paramagnetism we can describe H (c2)(T) and its anisotropy. In contrast, we find that Pauli paramagnetic pair breaking is not essential for Ba(Fe(0.93)Co(0.07))(2)As(2). For this electron-doped compound, the data support a H (c2)(T) dependence that can be described by the Werthamer-Helfand-Hohenberg model for H aEuro- ab and a two-gap behavior for H aEuro- c.
DOI10.1134/s0021364011110038
Alternate JournalJetp Lett.