Insensitivity of the band structure of substituted SrRuO3 as probed by Seebeck coefficient measurements

The influence of substitutions and vacancies in a unique 4d itinerant ferromagnet SrRuO3 are studied by thermoelectric power, resistivity, and magnetic measurements. Despite large changes of the Curie temperature, ordered magnetic moment, and conductivity, the thermoelectric power (Seebeck coefficient S) is much less sensitive to substitutions. Below about T < 100 K, i.e., below T-C, S is proportional to T as for other metallic oxides indicating that S is controlled by the electronic diffusion enhanced by electronic correlations. For T > T-C, the S values are much less dependent on T as if only the spin degeneracy term in the high-T expression of the Heikes formula is controlling the behavior. For all the compounds with calculated Ru valency between similar to 3.8 and similar to 4, the values of S at 300 K are approximately constant, but they decrease when the valency exceeds similar to 4. The practically constant value of S at 300 K shows that the density of states of SrRuO3 is relatively unaffected by the various substitutions and defects studied here. Furthermore, the peculiar role of Cr, which enhances the ferromagnetism, is confirmed by thermopower measurements.