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arXiv · 0904.1418

Anisotropy of the upper critical field in a Co-doped BaFe2As2 single crystal

M. Kano·Y. Kohama·D. Graf·F. F. Balakirev·A. S. Sefat·M. A. McGuire·B. C. Sales·D. Mandrus·S. W. Tozer
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Abstract

The temperature dependence of the upper critical magnetic field (Hc2) in a BaFe1.84Co0.16As2 single crystal was determined via resistivity, for the inter-plane (H^ab) and in-plane (H//ab) directions in pulsed and static magnetic fields of up to 60 T. Suppressing superconductivity in a pulsed magnetic field at 3He temperatures permits us to construct an H-T phase diagram from quantitative Hc2(0) values and determine its behavior in low temperatures. Hc2(0) with H//ab (Hc2//(0)) and H^ab (Hc2^(0)) are ~ 55 T and 50 T respectively. These values are ~ 1.2 - 1.4 times larger than the weak-coupling Pauli paramagnetic limit (Hp = 1.84 Tc), indicating that enhanced paramagnetic limiting is essential and this superconductor is unconventional. While Hc2//ab is saturated at low temperature, Hc2 with H^ab (Hc2^) exhibits almost linear temperature dependence towards T = 0 K which results in reduced anisotropy of Hc2 in low temperature. The anisotropy of Hc2 was ~ 3.4 near Tc, and decreases rapidly with lower temperatures reaching ~ 1.1 at T = 0.7 K.

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M. Kano, Y. Kohama, D. Graf, F. F. Balakirev, A. S. Sefat, M. A. McGuire, B. C. Sales, D. Mandrus, S. W. Tozer. 2009-04-13. Anisotropy of the upper critical field in a Co-doped BaFe2As2 single crystal. https://doi.org/10.1143/jpsj.78.084719

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