Near-Room-Temperature Antiferromagnetic Ordering in the Quadruple-Perovskite Sr4NaRu3O12

We report the synthesis, structure, and magnetic properties of two 1:3 ordered quadruple perovskites Sr4MRu3O12 (M = Li and Na). Sr4NaRu3O12 crystallizes in the centrosymmetric space group R3̅, and Sr4LiRu3O12 appears to be isostructural to the Na compound based on the PXRD data. In Sr4NaRu3O12, both Na and Ru are predominantly ordered at the B sites (here Na/Li and Ru), and the structure contains only corner-connected RuO6 and NaO6 octahedra. This atomic ordering also leads to a rather large unit cell with a = 11.25 Å and c = 27.6 Å compared to the basic 12R structure (a ∼ 5.5 Å and c ∼ 27 Å). Magnetic measurements reveal that Sr4NaRu3O12 undergoes a magnetic transition to an antiferromagnetic state below TN ∼ 265 K, confirmed by DSC and neutron diffraction. The Ru moments show a collinear antiferromagnetic spin alignment along the hexagonal c-axis with a propagation vector k = (0, 0, 1.5). Interestingly, those Ru moments lying on the 3-fold roto-inversion do not significantly contribute to the magnetic order, since they are located between antiferromagnetically coupled Ru atoms and are therefore highly frustrated. Sr4LiRu3O12 shows a magnetic anomaly around 110 K, possibly associated with competing ferromagnetic and antiferromagnetic interactions.