Abstract
A novel magnetic pair-making interaction between Mn and Ru shows a strong correlation between the magnetic ordering and electronic transport, which was well exemplified in the investigation of bulk polycrystalline samples of La0.7Pb0.3Mn1⊟xRuxO3 and La0.6Pb0.4Mn1⊟xRuxO3, where 0.0 ≤ x ≤ 0.4. The metal-insulator transition (Tρ) complementing the Curie temperature (Tc) was observed up to 30% of Ru in La0.7Pb0.3Mn1⊟xRuxO3, and extended up to 40% of Ru in La0.6Pb0.4Mn1⊟xRuxO3, showing a unique double-exchange ferromagnetic exchange interaction between Mn and Ru ions. An upturn in resistance due to charge carrier localization at low temperatures (T<0.5 Tc) for more than 20% Ru doping was due to a dominant hole carrier density contribution rather than to grain boundary effects as inferred from the scanning electron microscopy and energy dispersive x-ray studies of the samples sintered at 1200 and 1400 °C. The charge localization effect of the eg electrons was removed by tuning the hole carrier density as demonstrated in the La0.6Pb0.4Mn1⊟xRuxO3 samples. Long range correlations between magnetism and transport in this series was attributed to the presence of mixed valence Ru(IV/V) and Mn(III)/(IV) pair, which shows a unique double exchange mediated interaction.
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