Correlations between micro- and nanostructures and magnetic transitions in the Ru-doped Sm0.2Ca0.8MnO3 manganites

The electron microscopy study of the Ru-doped manganites Sm0.2Ca0.8Mn1-xRuxO3 (0 less than or equal to x less than or equal to 0.10) shows that the magnetic properties of these materials are strongly correlated to their microstructure, Charge ordering induced by Mn-site doping is shown for the first time, in contrast to what is generally observed. It is shown that Ru-doping paradoxically favors the simultaneous development of ferromagnetic orthorhombic domains and charge-ordered antiferromagnetic domains at low temperature, starting from a monophasic orthorhombic paramagnetic sample at room temperature. This structural phase separation phenomenon at low temperature is explained in terms of two antagonist effects introduced by Ru5+ Substitution: ferromagnetic superexchange interactions and Mn valency. (C) 2000 Academic Press.