Anisotropic magnetic and superconducting properties of CaFe2-xCoxAs2 (x=0, 0.06) single crystals

We report on anisotropic dc magnetic susceptibility chi(T), electrical resistivity rho(T), and heat-capacity C(T) measurements on the single crystals of CaFe2-xCoxAs2 for x=0 and 0.06. Large-sized single crystals were grown by the high-temperature solution method with Sn as the solvent. The spin-density wave (SDW)/structural transition observed at 170 K in the pure CaFe2As2 compound is suppressed for the Co-doped sample CaFe1.94Co0.06As2 and superconductivity is observed at similar or equal to 17 K. The superconducting transition has been confirmed from the magnetization and electrical resistivity studies. The Fe-57 Mossbauer spectrum in CaFe2As2 indicates that the SDW ordering is incommensurate with the crystal lattice. In the Co-doped sample, a prominent paramagnetic line at 4.2 K is observed indicating a weakening of the SDW state.