Ferrimagnetism and metal-insulator transitions in the LaMn<SUB>x</SUB>Ru<SUB>1-x</SUB>O<SUB>3</SUB> perovskites

We describe the synthesis, structure, magnetic and electrical properties of solid solutions of nominal composition, LaMnxRu1-xO3 (0&lt;x&lt;1). All the members crystallize in the GdFeO3-perovskite structure where Mn/Ru are randomly distributed at the octahedral sites. Weight losses due to hydrogen reduction, recorded using thermogravimetry, suggest considerable nonstoichiometry arising from partial oxidation of Mn/Ru to the tetravalent state. The nonstoichiometry is most likely accommodated by creating vacancies both at A and B sites of the perovskite structure, just as it occurs in LaMnO3+y. Members with x &#8805;0.50 exhibit a short-range ferro/ferrimagnetic order below 150 K that is likely due to MnIII/VI---O---RuIII (ferrimagnetic) and MnIII---O---MnVI (ferromagnetic) interactions in the perovskite structure. All the members are semiconducting including the x=0.05 member, suggesting that a metal-insulator transition occurs in the LaMnxRu1-xO3 system for x &#8804;0.05