N. D. Zhigadlo, S. Weyeneth, S. Katrych, P. J. W. Moll, K. Rogacki, S. Bosma, R. Puzniak, J. Karpinski, B. Batlogg
Single-crystalline samples of the LnFeAsO (Ln1111, Ln = Pr, Nd, and Sm) family with lateral dimensions up to 1 mm were grown out of NaAs and KAs flux using the cubic anvil high-pressure and high-temperature technique. The obtained crystals are of good structural quality and become superconducting when O is partially substituted by F (PrFeAsO1-xFx and NdFeAsO1-xFx) or when Fe is substituted by Co (SmFe1-xCoxAsO). Single crystals of SmFe1-xCoxAsO with maximal Tc up to 16.3 K for x = 0.08 were grown for the first time. Based on magnetization measurements, we estimate the temperature dependence and anisotropy of the upper critical field and the critical current density of underdoped PrFeAsO0.7F0.3 crystal with Tc = 25 K. The superconducting state properties of the SmFe1-xCoxAsO crystals with maximum Tc of 16.3 K are comparable to the properties of the SmFeAsO1-xFx crystals with much higher Tc. The upper critical field estimated from resistivity measurements is anisotropic with slopes of -8.7 T/K (H // ab-plane) and -1.7 T/K (H // c-axis) at temperatures far below Tc. The upper critical field anisotropy in the vicinity of Tc is around 8 and decreases with decreasing temperature. The critical current density is as high as 109 A/m2 at 2 K in magnetic fields up to 7 T.
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http://arxiv.org/abs/1208.6207
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