Identification of complex energy hierarchy in the coupled trimer spin system Ba4LuRu3O12

The weakly coupled spin cluster systems provide a fertile ground to study both zero-dimensional quantum and three-dimensional collective magnetism. Such spin cluster systems feature that the lower-energy magnetic excitations, including transverse and longitudinal magnon modes, emerge with gapped localized excitations concomitantly. The newly discovered trimer spin system Ba4LuRu3O12 constitutes Ru3O12 trimers made of three face-sharing RuO6 octahedra. The magnetic susceptibility of Ba4LuRu3O12 shows an antiferromagnetic order at TN = 8 K. However, the Curie-Wiess analysis of the magnetic susceptibility reveals that the local spin alignment of the Ru3O12 trimers varies with temperature. With the aid of inelastic neutron scattering, we will elucidate the energy-level scheme of the interacting spin trimer system and the underlying mechanism for the alteration of the spin configuration.