We investigate the Sn-substitution effect on the thermoelectric transport properties of the layered cobaltite ${\left[{\mathrm{Ca}}_2{\mathrm{CoO}}_3\right]}_{0.62}\left[{\mathrm{CoO}}_2\right]$ 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.

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• Pseudogap
• Seebeck effect
• Spin density waves
• Thermoelectric effects
• Thermoelectrics
• Thermopower
• Oxides
• Magnetization measurements
• Resistivity measurements
• X-ray diffraction