Long-Range Antiferromagnetic Ordering in the Novel Magnetically Frustrated Rock Salt Oxide System: Li₃Mg₂RuO₆

The new ruthenate, Li 3 Mg 2 RuO 6, was synthesized in polycrystalline form by a solid-state method. The crystal structure of Li 3 Mg 2 RuO 6 was refined from powder neutron diffraction data in the orthorhombic Fddd space group in an ordered NaCl structure type with a = 5.8759 (2) Å, b = 8.4206 (1) Å, and c = 17.6455 (5) Å. The Ru 5+ ( S = 3/2) sublattice shows a unique topology, which consists of chains of edge-sharing triangles interconnected by corner sharing and thus there exists the potential for geometric magnetic frustration. This is the first time that magnetic behavior of a material with such sublattice has been investigated. The isostructural, nonmagnetic Li 3 Mg 2 NbO 6 was prepared as the lattice match for the heat capacity analysis. The temperature-dependent magnetic susceptibility, heat capacity, and neutron diffraction data reveal that the system undergoes a long-range AFM ordering below 17 K but also provide evidence for short-range spin correlations well above T N . The magnetic frustration index, f ≈ 109/17 = 6.4 suggests that the system is geometrically frustrated. Spin dimer analysis of the magnetic exchange interactions supports this characterization. Comparisons are made with other materials containing the Ru 5+ ion on geometrically frustrated lattices.