Impurity-induced spin density wave in the thermoelectric layered cobaltite <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mo>[</mml:mo> <mml:msub> <mml:mi>Ca</mml:mi> <mml:mn>2</mml:mn> </mml:msub> <mm

We investigate the Sn-substitution effect on the thermoelectric transport properties of the layered cobaltite ${[{\mathrm{Ca}}_{2}{\mathrm{CoO}}_{3}]}_{0.62}[{\mathrm{CoO}}_{2}]$ single crystals, which exhibit a nonmonotonic temperature variation of the electrical resistivity and the Seebeck coefficient owing to the complex electronic and magnetic states. We find that the onset temperature of the short-range spin-density-wave (SDW) formation increases with the substituted Sn content, indicating the impurity-induced stabilization of the SDW order, reminiscent of the disorder/impurity-induced spin order in the cuprate superconductors. The Seebeck coefficient is well related to such impurity effects, as it is slightly enhanced below the onset temperatures, implying a decrease in the carrier concentration due to a pseudogap formation associated with the SDW ordering. We discuss the site-dependent substitution effects including earlier studies, and suggest that substitution to the conducting ${\mathrm{CoO}}_{2}$ layers is essential to increase the onset temperature, consistent with the impurity-induced SDW picture realized in the conducting layers with the cylindrical Fermi surface.