Abstract
The competition between interatomic Ru–O–Ru interactions responsible for itinerant-electron ferromagnetism in SrRuO 3 and intraatomic spin–orbit coupling that suppresses some Ru–O–Ru magnetic interactions in CaRuO 3 so as to prevent long-range magnetic order has been further tested by investigating the double perovskites La 2RuZnO 6, La 2RuCoO 6, La 2TiCoO 6, and the solid solution Ca 2−2 x La 2 x Ru 2− x Co x O 6 (0.0⩽ x⩽1.0). The paramagnetic state of the low-spin, localized Ru 4+:t 4e 0 configuration of LaRuZnO 6 undergoes a progressive transition on lowering the temperature to a non-magnetic state ( J=0) as a result of spin–orbit coupling, λ L· S. Comparison of the susceptibilities of La 2RuCoO 6 and La 2TiCoO 6 shows a similar behavior with long-range antiferromagnetic cobalt ordering via non-magnetic RuO 6/2 and TiO 6/2 bridges. Comparison is also made of the effect of substituting Ga for Ru in CaRuO 3 with the effect of other dopants M in CaRu 1− x M x O 3. The evolution of transport properties in Ca 2−2 x La 2 x Ru 2− x Co x O 6 is also presented.
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