Random singlet-like state in the dimer-based triangular antiferromagnet Ba6 Y2Rh2Ti2 O17-δ

We present the magnetic, thermodynamic, and muon spin relaxation (μSR) results of the dimer-based triangular antiferromagnet Ba6Y2Rh2Ti2O17-δ. The magnetic susceptibility data show the sub-Curie-Weiss behavior χ(T)·T-αχ below 100 K, suggesting random magnetism. The isothermal magnetization results reveal the presence of weakly interacting structural orphan spins about 6.1% at 2 K, arising from the oxygen deficiency. The comprehensive μSR experiments exhibit the coexisting relaxing and nonrelaxing components along with the thermally activated behavior in the muon spin relaxation rate, reflecting the fluctuating orphan spins in the dimer singlet background. In addition, we observe the scaling behavior of M(H,T) in H/T and Pz(t) in t/HLF with the scaling exponents αχ=αM=0.75 and αμ=0.72, respectively, but not for the magnetic specific heat data. The failure of the scaling relation in Cm(H,T)/T implies low-energy excitations dressed by the conventional orphan spins. Based on these observations, we find that the magnetic ground state resembles random singlets and discuss the possible configurations of the spin dimer unit Rh2O9. Our results shed light on the role of quenched disorder in the dimer-based frustrated magnets.