Direct evidence for double-exchange coupling in Ru-substituted La0.7Pb0.3Mn1-xRuxO3, 0.0 ≤ x ≤ 0.4

The La0.7Pb0.3Mn1-xRuxO3 (0.0less than or equal to x less than or equal to 0.4) system shows an innate relationship between Mn and Ru ions by a unique double-exchange mediated transport behavior. This is exonerated by the coexistence of T-p and T-c (range 330 K-245 K for 0.0 less than or equal to x less than or equal to 0.4). For Ru > 30%, the hole carrier mass influences the transport property. X-ray absorption spectra suggest that the T-c-T-p match is due to the transport mediated by the Mn3+/ Mn4+ <-->Ru4+/Ru5+ redox pair and also due to the broad low-spin Ru:4d conduction band. For x> 0.2, T< 0.5 T-c obeys a modified variable-range hopping model, where kT(0) proportional to( M/M-s)(2), suggesting a random magnetic potential which localizes the charge carriers.