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

The La0.7Pb0.3Mn 1 − x Ru x O3 (0.0 ≤ x ≤ 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 Tp and Tc (range 330 K–245 K for 0.0 ≤ x ≤ 0.4). For Ru > 30%, the hole carrier mass influences the transport property. X-ray absorption spectra suggest that the Tc-Tp 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 < 0.5Tc obeys a modified variable-range hopping model, where kT0 (M/Ms)2, suggesting a random magnetic potential which localizes the charge carriers.