Dy–4f coupling to 4d/5d dimer magnetism: a comparative µSR study of 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, i.e., Ba3DyIr2O9 and Ba3DyRu2O9, the structures host face-sharing M'-M' (Ir-Ir/Ru-Ru) magnetic dimers, providing a platform to contrast 5d (Ir) and 4d (Ru) spin orbit physics. 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 mechanism by which Dy 4f anisotropy differentiates the Ru and Ir dimer networks is unclear. We propose zero- and longitudinal-fields muSR studies to investigate relaxation rates (T), internal fields Bint, and magnetic volume fraction Vm, providing a decisive local test of static order versus slow dynamics in this Dy-fixed 4d/5d pair. The measurements will establish whether the Ru analogue exhibits larger Bint, larger, and fully developed static order relative to the Ir analogue. (A complementary WISH diffraction study is planned to determine magnetic structures.)