Ru-Induced Ferromagnetism and Metallicity in Mn(IV)-Rich Manganites Ln0.4Ca0.6MnO3

The doping of Mn sublattice by Ru in the Mn(IV)-rich manganites Ln0.4Ca0.6MnO3 (Ln: Lanthanide; Ln=La, Pr, Nd, Sm) induces an insulator-to-metal transition which is not obtained by Cr doping. The appearance of metallicity and ferromagnetism in these Ru-doped manganites is explained in the frame of the phase separation scenario, Ru forming ferromagnetic (FM) clusters, which extend as the Ru content increases. The particular aptitude of Ru for promoting a FM metallic state is discussed, on the basis of Ru(V) and Ru(IV) oxidation states, which are isoelectronic to Mn(IV) and Mn(III), respectively. Magnetoresistance is also evidenced and discussed.