For the investigations of intrinsic properties relevant for applications of FeAs based superconductors studies on single crystals are necessary. LnFeAsO  (Ln=La, Pr, Nd, Sm, Gd) single crystals were grown from flux at high-pressure of 30 kbar. Two kind of fluxes have been used: NaCl/KCl and NaAs/KAs. An overview of the basic superconducting properties measured on single crystals of LnFeAsO will be presented.  LnFeAsO compounds show the highest T_c up to 55K and the highest upper critical fields. Superconductivity in LnFeAsO single crystals has been induced by partial substitution of O by F or by H, Sm by Th, Fe by Co, As by P or by oxygen deficiency. Single crystal structure investigations show structure modifications due to substitutions which are linked to superconducting properties. Especially substitution of H for O is important, because it allows much higher doping rate than substitution of F for O. Detailed study of the transport properties of SmFeAs(O,F) single crystals reveals a promising combination of high (> 2 10⁶ A/cm²) and nearly isotropic critical current densities up to 30 T at low temperatures. In the frame of these studies new superconductor related to LnFeAsO, but with much larger c lattice parameter with T_c up to 40K has been discovered. Properties of new superconductor will be presented.

1. J. Karpinski, Phil. Mag. 92 (2012) 2662.
2. Philip J.W. Moll et al., Nature Mat. 12 (2012) 134.

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