Magnetic impurities in the pnictide superconductor Ba1-xKxFe2As2

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Mukhopadhyay, Sutirtha
Oh, Sangwon
Mounce, A. M.
Lee, Moohee
Halperin, W. P.
Ni, Ni
Bud'ko, S. L.
Reyes, A. P.
Kuhns, P. L.
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Institute of Physics and Deutsche Physikalische Gesellschaft
Canfield, Paul
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Nuclear magnetic resonance (NMR) measurements have been performed on single crystals of Ba1−xKxFe2As2 (x=0, 0.45) and CaFe2As2 grown from Sn flux. The Ba-based pnictide crystals contain significant amounts of Sn in their structure, ∼1%, giving rise to magnetic impurity effects evident in the NMR spectrum and in the magnetization. Our experiments show that the large impurity magnetization is broadly distributed on a microscopic scale, generating substantial magnetic field gradients. There is a concomitant 20% reduction in the transition temperature, which is most likely due to magnetic electron scattering. We suggest that the relative robustness of superconductivity (x=0.45) in the presence of severe magnetic inhomogeneity might be accounted for by strong spatial correlations between impurities, such as clustering on the coherence length scale.
This article is published as Mukhopadhyay, Sutirtha, Sangwon Oh, A. M. Mounce, Moohee Lee, W. P. Halperin, N. Ni, S. L. Bud'ko, P. C. Canfield, A. P. Reyes, and P. L. Kuhns. "Magnetic impurities in the pnictide superconductor Ba1− xKxFe2As2." New Journal of Physics 11, no. 5 (2009): 055002. DOI: 10.1088/1367-2630/11/5/055002. Copyright 2009 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. CC BY 3.0. Posted with permission.