We measured thermal conductivity $\kappa$, thermoelectric power $S$, and electric conductivity $\sigma$ of ${\mathrm{La}}_{5/8-x}{\mathrm{Pr}}_x{\mathrm{Ca}}_{3/8}{\mathrm{MnO}}_3$, showing an intricate interplay between metallic ferromagnetism (FM) and charge ordering (CO) instability. The change of $\kappa$, $S$, and $\sigma$ with temperature $\left(T\right)$ and $x$ agrees well with the effective medium theories for binary metal-insulator mixtures. This agreement clearly demonstrates that with the variation of $T$ as well as $x$, the relative volumes of FM and CO phases drastically change and percolative metal-insulator transition occurs in the mixture of FM and CO domains.

• Received 2 June 1999

DOI:https://doi.org/10.1103/PhysRevLett.84.2961