Single crystals of superconducting SmFeAsOHx: Structure and properties

We report the synthesis, structure, and superconducting properties of single crystals of SmFeAsOHx. The crystals were grown at high pressure and high temperature using a cubic anvil technique. H-1-NMR studies confirm the presence of H atoms in the samples. Single crystal x-ray diffraction analyses demonstrate a remarkable disorder in the Sm2O2 layers induced by hydrogen incorporation and reveal that the H positions are compatible with a H2O-like geometry inside the crystals. We have measured the magnetotransport properties of SmFeAsOHx single crystals with x = 0.07, 0.11, and 0.16 in magnetic field up to 16 T, oriented along the two main crystallographic directions. The results show an increase of the critical temperature with hydrogen content. The zero-temperature upper critical fields and the magnetic anisotropy are calculated as a function of the hydrogen content. SmFeAsOHx crystals present significantly higher upper critical fields and magnetic anisotropies compared to SmFeAsO1-x F-x compounds.