We report the magnetic susceptibility, specific heat, and muon spin relaxation results of the $5d^1$ double perovskite ${\mathrm{Ba}}_2{\mathrm{YWO}}_6$. The dc magnetic susceptibility shows two distinct Curie-Weiss regimes and a sub-Curie-Weiss increase $T^{-n}$ with $n=0.75\left(1\right)$ for $T=3\text{–}100$ K, alluding to the presence of random magnetism. The ac magnetic susceptibility reveals a spin freezing at $T_f\sim 0.3$ K with the activation energy of $\mathrm{\Delta }/k_B=27.6$ K. The specific heat data exhibit the pseudogap behavior at 25 K and the subsequent power-law dependence with decreasing temperature, indicating the gradual spin freezing with the quenching of orbital fluctuations. However, the muon spin relaxation data display only a weak muon spin depolarization with lacking long-range magnetic ordering down to 26 mK. Taken together, our results suggest that ${\mathrm{Ba}}_2{\mathrm{YWO}}_6$ is the proximate realization of a random spin-orbit dimer state.

• Received 19 February 2021
• Revised 24 May 2021
• Accepted 7 June 2021

DOI:https://doi.org/10.1103/PhysRevB.103.224430