Investigation of true magnetic ground states in the trimer based hexagonal perovskite oxides Ba4TaM3O12 (M = Ir, Ru) using muon-spin-rotation/relaxation (µSR)

The heavier 4d and 5d transition metal based hexagonal perovskite oxides with face-sharing octahedra and edge-sharing triangular network can serve as a fertile avenue for exploring a rich spectrum of frustrated quantum magnetism, including quantum spin liquid (QSL), In such a background, we here experimentally investigate a new series of compounds Ba4TaM’3O12 (M’ = Ir, Ru) belonging to the relatively poorly studied 12L-hexagonal quadrupole perovskite family comprising of the M’3O12 trimer units. Despite substantial antiferromagnetic exchange between the local moments, our combined dc, ac susceptibility, and specific heat data clearly refute magnetic long-range ordering transition or a spin-glass freezing down to 50 mK in these compounds. This together with a combined T-linear and quadratic T-dependence of specific heat at low-T could indicate gapless excitations. All these point to the candidate QSL materials, which therefore warrants in-depth microscopic local probe muon-spin-relaxation/rotation investigations to ascertain the true magnetic ground states in both these materials.