Effect of Co-doping on the resistivity and thermopower of SmFe _1-xCo_xAsO (0.0≤x≤0.3)

We report structure, electrical resistivity and thermopower of polycrystalline SmFe_1-x Co_xAsO samples for 0.0 ≤ x ≤ 0.3. The XRD data revealed full Co substitution at Fe-site with slight compression of the unit cell. Resistivity data showed that the spin-density wave observed at 130 K for x = 0 is suppressed when x = 0.05, above which superconductivity emerges due to injection of mobile electrons, supporting the substitution of Co³⁺ at Fe²⁺ site but disappears for x = 0.3. The thermopower (S) data indicate that the majority of charge carriers is electron-like and its value reaches -81 μV/K (at 300 K) for x = 0.3. Noticeable deviations from the expected linear behavior in S(T) at low temperatures and S/T against temperature curves at intermediate temperatures were observed. These observations were interpreted on the basis of nested Fermi surface and Umklapp processes.