Spin dynamics and 4f-dimer coupling in Dy-based hexagonal perovskites Ba3DyRu2O9 and Ba3DyIr2O9

The dimer-based 6H-hexagonal triple perovskites oxides, with the general formula Ba3MM'2O9 (M = rare Earth; M' = Ir or Ru) are key quantum materials exhibiting complex magnetism. With Dy3+ on the M site in Ba3DyIr2O9 and Ba3DyRu2O9, the structures host face-sharing M-M(Ir-Ir/Ru-Ru) magnetic dimers, which provide a platform to contrast 5d (Ir) and 4d (Ru) systems that exhibit exotic magnetism arising from competing exchange and spin orbit interactions. Notably, bulk magnetization data reveal a striking divergence in the highest-temperature magnetic anomalies:~27 28 K for Ba3DyRu2O9 versus ~8.9 K for Ba3DyIr2O9. This contrast suggests 4f anisotropy of Dy3+ reinforces exchange in the Ru dimer network but competes with SOC-driven anisotropic exchange in the Ir dimer network. However, the microscopic mechanism remains unclear and detailed information on the magnetic excitations and crystal electrical field (CEF) of Dy3+ ions of these two compounds are highly desirable. We therefore propose inelastic neutron scattering (INS) on MARLIN to quantify the underlying spin wave and CEF energy scales that reveal the contrasting roles of 4f interactions and 4d/5d magnetism in both, by directly probing their spin wave and, crystal-field transitions. Together with our planed WISH (static magnetic structure) and EMU (local spin relaxation), MARLIN will complete a multi-technique picture linking structure, dynamics, and local fields in Dy-based hexagonal dimers.