Anisotropic magnetic and superconducting properties of pure and Co-doped CaFe2As2 single crystals
Abstract
We report anisotropic dc magnetic susceptibility (T), electrical resistivity (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. For the pure compound with x = 0, a high temperature transition at 170 K is observed which is attributed to a combined spin density wave (SDW) ordering and a structural phase transition. On the other hand, for the Co-doped samples for x = 0.06, the SDW transition is suppressed while superconductivity is observed at 17 K. The superconducting transition has been confirmed from the magnetization and electrical resistivity studies. The 57Fe M\"ossbauer spectrum in CaFe2As2 indicates that the SDW ordering is incommensurate. In the Co-doped sample, a prominent paramagnetic line at 4.2 K is observed indicating a weakening of the SDW state.