We report anisotropic dc magnetic susceptibility Ο(T), electrical
resistivity Ο(T), and heat capacity C(T) measurements on the single
crystals of CaFe2βxβCoxβAs2β 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 β17 K. The superconducting transition
has been confirmed from the magnetization and electrical resistivity studies.
The 57Fe M\"ossbauer spectrum in CaFe2βAs2β 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.Comment: 4 pages 5 figures. Submitted to Phys. Rev.