Abstract
Double exchange mediated magnetism and transport properties are exemplified in two-dimensional layered manganites, La1.2Ca1.8Mn2O7. We demonstrate here the role of ruthenium in showing increased metal-insulator transition temperature, T-P and Curie temperature T-c, by about 15 K when Ru is substituted up to 10% (x=0.2) at the Mn site. We discuss these unique features based on the existence of a redox ionic pair involving Mn3+/Mn4+<->Ru4+/Ru5+ up to xsimilar to0.2. Beyond the critical level (xsimilar to0.2), Ru exists mostly in Ru4+ oxidation state leading to a weak double exchange interaction. We document here, an enhanced T-c and T-P in the layered manganites despite the disorder induced at the B site. (C) 2002 American Institute of Physics.