Synthesis, structure, and properties of Ba₉Co₃Se₁₅ with one-dimensional spin chains

A new compound with one-dimensional spin chains, Ba₉Co₃Se₁₅, was synthesized under high pressure and high temperature conditions and systematically characterized via structural, transport and magnetic measurements. Ba₉Co₃Se₁₅ crystallizes in a hexagonal structure with the space group P-6c2 (No. 188) and lattice constants of a =b = 9.6765 Å and c = 18.9562 Å. The structure consists of trimeric face-sharing octahedral CoSe₆ chains, which are arranged in a triangular lattice in the ab-plane and separated by Ba atoms. The distance of the nearest neighbor of CoSe₆ chains is very large, given by the lattice constant a= 9.6765 Å. The Weiss temperature T_θ associated with the intra-chain coupling strength is about -346 K. However, no long-range magnetic order but a spin glass transition at ~3 K has been observed. Our results indicate that the spin glass behavior in Ba₉Co₃Se₁₅ mainly arises from the magnetic frustration due to the geometrically frustrated triangular lattice.