Investigation of electronic transport and magnetic properties in Ca₂-₂xLa₂xRu₂-xCoxO₆

Ca2-2xLa2xRu2-xCoxO6 ( 0.0 ≤ x ≤ 1.0 ) is prepared by a "Polymerizable-Complex Method." Electronic transport and magnetic properties are measured to show that the system becomes semiconducting at x ≈ 0.1 and goes through long-range antiferromagnetic ordering at x ≈ 0.4. The proximity in Néel temperature TN of La2RuCoO6 to that of La2TiCoO6 previously reported suggests that the magnetic moment of Ru4+ becomes quenched as temperature decreases. This suppression is explained by a theory that due to (1) the strong spin-orbit coupling ( large spin-orbit coupling constant [Greek small letter lambda] ) present in Ru4+ ions and (2) the sign inversion of [Greek small letter lambda] suggested by Kanamori, the Ruions favors the antiparallel alignment of L and S leading to J = 0. Based on (1) the similarity in the inverse magnetic susceptibility 1/[Greek small letter chi] (T) between CaRuO3 and La2RuZnO6 and (2) the presence of features in CaRuO3 commonly associated with phase fluctuations, the suppression of magnetic moment in Ru4+ is proposed to be responsible for the absence of long-range magnetic ordering in CaRuO3 as well. Finally, the appearance of long-range ferromagnetic ordering in CaRu1-xMxO3 is explained by (1) the degree of hybridization of the Ru4+/Ru5+ redox couple with empty d orbitals and (2) the formation of ferrimagnetic clusters from t2g 3-O- t2g 3 interactions between dopants and localized Ru5+: t2g 3eg 0 configurations.