Thermopower of giant magnetoresistive oxide system La1-xCuxMnO3 (0.1<=x<=0.4)

The thermopower (Seebeck coefficient, S) of the perovskite oxide system La1-xCaxMnO3 for compositions 0.1 less than or equal to x less than or equal to 0.4 has been measured for 4.5 K less than or equal to T less than or equal to 360 K. The observed S is rather complex and points to a number of processes occuring in these materials. We suggest a scheme to analyze the data. S depends on the Mn4+ content and shows a systematic change to more negative value as x (i.e, Mn4+ content) increases. A large negative peak in S at around 25 K has been observed suggesting the existance of a strong inelastic scattering mechanism hitherto not seen in this material.