Ferrimagnetism and metal-insulator transitions in the LaMnxRu1-xO3 perovskites

We describe the synthesis, structure, magnetic and electrical properties of solid solutions of nominal composition, LaMnxRu1-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 LaMnO3+y. Members with x greater than or equal to 0.50 exhibit a short-range ferro/ferrimagnetic order below 150 K that is likely due to Mn-III/VI-O-Ru-III (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 LaMnxRu1-xO3 system for x less than or equal to 0.05. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.