Ferrimagnetism and metal-insulator transitions in the LaMn_xRu_1-xO₃ perovskites

Abstract

We describe the synthesis, structure, magnetic and electrical properties of solid solutions of nominal composition, LaMn_xRu_1-xO₃ (0<x<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 LaMnO_3+y. Members with x ≥0.50 exhibit a short-range ferro/ferrimagnetic order below 150 K that is likely due to Mn^III/VI---O---RuIII (ferrimagnetic) and Mn^III---O---Mn^VI (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 LaMn_xRu_1-xO₃ system for x ≤0.05.