Influence of Ru-doping on structure, defect chemistry, magnetic   interaction and carrier motion of the La1-xNaxMnO3+delta manganite
  In this work we report a structural, electrical and magnetic characterization of the La1-xNaxMn1-yRuyO3+d (LNMRO) system with x = 0.05, 0.15 and y = 0, 0.05, 0.15, also comprising an investigation of the role of the oxygen content on the related redox properties. The experimental investigation has been realized with the aid of X-ray powder diffraction, electron microprobe analysis, thermogravimetry, electrical resistivity and magnetization measurements, and electron paramagnetic resonance. We demonstrate that the effect of ruthenium doping on the studied LNMRO compounds is not only directly related to the Ru/Mn substitution and to the Ru oxidation state but also indirectly connected to the oxygen content in the sample. Our data show that ruthenium addition can improve electrical and magnetic properties of non-optimally (low) cation doped manganites, causing an increase of the TC value and the insurgence of MR effect, as observed for the x = 0.05 and y = 0.05 sample. 
Lorenzo Malavasi, Maria Cristina Mozzati, Cristina Tealdi, Carlo Bruno   Azzoni, and Giorgio Flor