Investigation of crystal field excitations in Ba3RRu2O9 (R= Tb, Nd)

The 4d-4f based magnetic materials have garnered a lot of interest due to competing magnetic exchange interactions. In the present proposal, we focus on Ba3TbRu2O9 and Ba3NdRu2O9 compounds of Ba3RRu2O9 (R is rare-earth) series. The hexagonal crystal structure of these compounds is quite interesting where Tb/Nd octahedra (Tb/NdO6) and Ru dimer (Ru2O9) form a triangular lattice in the ab plane. The dc magnetization study infers antiferromagnetic and ferromagnetic transitions in Ba3TbRu2O9 and Ba3NdRu2O9 compounds, respectively. The analysis of inverse susceptibility data of Ba3TbRu2O9 compound reveals the effective magnetic moment ~7.64 muB which is close to ~7.94 muB expected for Tb4+ (4f7) ions rather than that ~ 9.72 muB for Tb3+ (4f8) ions, indicating the Kramer’ ion character of Tb ions. The inverse susceptibility data of Ba3NdRu2O9 compound is better analyzed using a two-level model. The analysis reveals the splitting of energy levels under the crystal field and the calculated energy gap of ~16.5 meV is found close to the literature reported value of ~12.5 meV for isostructural Ba3YRu2O9 compound. However, a microscopic INS (inelastic neutron scattering) study is required to understand crystal field effect excitations in Ba3RRu2O9 (R= Tb, Nd) compounds, which has not been explored so far in these compounds. We propose a first comprehensive crystal-field-excitation study on Ba3TbRu2O9 and Ba3NdRu2O9 polycrystalline compounds.