Inelastic Neutron Scattering Study of Ru2O9 Dimers and Magnetic Ground States in Magnetodielectric Ba3R(R=Tb/Ho)Ru2O9

The series Ba3RRu2O9 (R= Rare-earth) containing Ru2O9 dimer got large attention due to its exotic magnetic, magnetoelectric and multiferroic behavior arising from Ru(4d)-R(4f) coupling. Specifically, the Ho and Tb members shows strong magnetodielectric (MD) coupling. In this series, the valence state of R is normally +3 which indicate average valance state of Ru is +4.5. In contrast, the Tb and Ru both having +4 state in Ba3TbRu2O9 makes the compound unique in this family. The compound Ba3TbRu2O9 orders at 10 K. However MD coupling far above 10 K is documented.Ru-ordering and Ru(4d)-Tb(4f) coupling seems to have significant role on MD behavior. In our previous TOF neutron diffraction study we observe a new magnetic phase at 50 K which is far above the the reported ordering temperature.Here, we aim to investigate the nature of the ground state and magnetic excitations, competting exchange interaction through INS.The high resolution of Merlin is required to perform such investigation.