Structures and Magnetic Properties of Double Perovskites A2LnMO6 and 6H-Perovskites Ba3LnRu2O9 (A = Sr, Ba; Ln = Y, Lanthanides; M = Nb, Ta, Ru)

Abstract

Abstract This account describes the synthesis, crystal structures and magnetic properties of double perovskites A2LnMO6 and 6H-perovskites Ba3LnRu2O9 (A = Sr, Ba; Ln = Y, lanthanides; M = Nb, Ta, Ru). The double perovskites A2LnMO6 have two kinds of cations, Ln and M, in the B site of the perovskite ABO3. These cations adopt the alternative ordered arrangement. Measurements of the magnetic susceptibility, specific heat, and powder neutron diffraction showed that all of the A2LnRuO6 compounds exhibited an antiferromagnetic transition at low temperatures and a complex temperature dependence of the magnetic susceptibility below their transition temperatures. In these compounds, the magnetic interaction between the Ln (4f electrons) and Ru (4d electrons) ions via the Ln–O–Ru pathway contributes greatly to their magnetic cooperative phenomena. The structural and magnetic studies for the 6H-perovskites Ba3LnRu2O9 show that the Ln cations occupy the corner-sharing octahedra (LnO6 octahedron) and the Ru cations occupy the face-sharing octahedra (Ru2O9 dimer). The Ba3LnRu2O9 compounds show a characteristic temperature-dependence of the magnetic susceptibilities, that is, a broad maximum at temperatures above 135 K and a magnetic transition at 5–15 K. These magnetic properties mainly reflect two kinds of the magnetic interactions: the interaction between Ln and Ru ions and that between Ru ions in the Ru2O9 dimer.