Interplay between the spin dimer and the triangular lattice in the 6H-perovskite system Ba3PrRu2O9

The recently discovered 6H-perovskite Ba3PrRu2O9 is comprised of the triangular layers formed by Pr4+ ions and the Ru2O9 dimer units located between the triangular layers. Three different exchange interactions (intra-dimer, intra-triangle, and between a triangular plane and a dimer) in Ba3PrRu2O9 provide an intriguing platform to study the interplay between the spin dimer and the triangular lattice. The magnetic susceptibility of Ba3PrRu2O9 exhibits a broad maximum at around 380 K and an antiferromagnetic ordering at TN = 10.5K, suggesting spin-gapped states arising from the Ru2O9 dimers and the ordering of the Pr spins, respectively. Thermodynamic measurements also support the long-range magnetic ordering of the Pr moments below TN. In this project, we will determine the arrangement of the spins within the Ru2O9 dimer and the underlying mechanism for the long-range magnetic ordering.