AgRuO₃, a Strongly Exchange-Coupled Honeycomb Compound Lacking Long-Range Magnetic Order

Quasi two-dimensional (2D) oxide-based honeycomb lattices have attracted great attention for displaying specific electronic instabilities, which give rise to unconventional bonding patterns and unexpected magnetic exchange couplings. The synthesis of AgRuO₃, another representative exhibiting unique structural properties, is reported here. The stacking sequence of the honeycomb layers (Ru₂O₆) differs from analogous precedents; in particular, the intercalating silver atoms are shifted from the middle of the interspaces and cap the void octahedral sites of the (□Ru₂O₆) slabs from both sides. This way, charge neutral, giant 2D “molecules” of Ag/Ru₂O₆/Ag result; a feature that significantly enhances the overall 2D character of AgRuO₃. Measurements of magnetization have revealed extremely strong magnetic exchange coupling to be present, surviving to a temperature as high as 673 K, which is the temperature of thermal decomposition. No indication for long-range magnetic order has, however, been observed. Theoretical analyses confirm the pronounced 2D character of the electronic system, and in particular reveal the inter-honeycomb layer coupling J_c to be distinctly weak.