Abstract
With the discovery of new superconducting materials, such as the iron pnictides1, exploring their potential for applications is one of the foremost tasks. Even if the critical temperature Tc is high, intrinsic electronic properties might render applications difficult, particularly if extreme electronic anisotropy prevents effective pinning of vortices and thus severely limits the critical current density, a problem well known for cuprates2,3,4,5. Although many questions concerning microscopic electronic properties of the iron pnictides have been successfully addressed5 and estimates point to a very high upper critical field6,7,8,9, their application potential is less clear. Thus, we focus here on the critical currents, their anisotropy and the onset of electrical dissipation in high magnetic fields up to 65 T. Our detailed study of the transport properties of SmFeAsO0.7F0.25 single crystals reveals a promising combination of high (>2×106 A cm−2) and nearly isotropic critical current densities along all crystal directions. This favourable intragrain current transport in SmFeAs(O, F), which shows the highest Tc of 54 K at ambient pressure10,11,12, is a crucial requirement for possible applications. Essential in these experiments are four-probe measurements on focused-ion-beam-cut single crystals with a sub-square-micrometre cross-section, with current along and perpendicular to the crystallographic c axis.
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Acknowledgements
We thank S. Katrych for carrying out X-ray analyses, and P. Gasser and K. Kunze for FIB assistance supporting this study. Work at NHMFL-LANL is carried out under the auspices of the National Science Foundation, Department of Energy and State of Florida. Electron Microscopy and FIB work was carried out at the Electron Microscopy ETH Zurich (EMEZ). This work has been supported by the Swiss National Science Foundation NCCR Materials with Novel Electronic Properties (MaNEP) and by the Polish Ministry of Science and Higher Education under the research project No. N N202 4132 33.
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P.J.W.M. and B.B. designed the experiment and wrote the paper. P.J.W.M. carried out the direct transport critical current experiments; the pulsed field magnetotransport was measured by P.J.W.M. and F.B. R.P., K.R. and B.B. measured magnetization and evaluated the magnetic critical currents jcmag. K.R. carried out the pinning analysis. N.D.Z. and J.K. grew the crystals.
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Moll, P., Puzniak, R., Balakirev, F. et al. High magnetic-field scales and critical currents in SmFeAs(O, F) crystals. Nature Mater 9, 628–633 (2010). https://doi.org/10.1038/nmat2795
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DOI: https://doi.org/10.1038/nmat2795
