Insensitivity of the band structure of substitutedSrRuO3as probed by Seebeck coefficient measurements

Abstract

The influence of substitutions and vacancies in a unique $4d$ itinerant ferromagnet $\mathrm{Sr}\mathrm{Ru}{\mathrm{O}}_{3}$ 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 $T<100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, 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 $\ensuremath{\sim}3.8$ and $\ensuremath{\sim}4$, the values of $S$ at $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ are approximately constant, but they decrease when the valency exceeds $\ensuremath{\sim}4$. The practically constant value of $S$ at $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ shows that the density of states of $\mathrm{Sr}\mathrm{Ru}{\mathrm{O}}_{3}$ 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.