Improved growth of Ln1111 superconducting crystals from NaAs/KAs flux

Single crystals of the LnFeAsO (Ln1111, Ln $=$ Pr, Nd, and Sm) family with lateral dimensions up to 1 mm were grown from NaAs and KAs flux using the cubic anvil high-pressure and high-temperature technique. The crystals become superconducting when O is partially substituted by F (PrFeAsO$_{\mathrm{1-x}}$F$_{\mathrm{x}}$ and NdFeAsO$_{\mathrm{1-x}}$F$_{\mathrm{x}})$ or when Fe is substituted by Co (SmFe$_{\mathrm{1-x}}$Co$_{\mathrm{x}}$AsO). In SmFe$_{\mathrm{1-x}}$Co$_{\mathrm{x}}$AsO the maximum $T_{\mathrm{c\thinspace }}$is 16.3 K for x $=$ 0.8. From transport and magnetic measurements we estimate the critical fields and their anisotropy, and we find these superconducting properties to be quite comparable to the ones in SmFeAsO$_{\mathrm{1-x}}$F$_{\mathrm{x}}$ with a much higher $T_{\mathrm{c}}$ of $\approx $ 50 K. The magnetically measured critical current densities are as high as 10$^{\mathrm{9}}$ A/m$^{\mathrm{2}}$ at 2 K up to 7 T, with indications of the usual ``fish tail'' effect.