One of the key questions concerning frustrated lattices that has lately emerged is the role of disorder in inducing spin-liquid-like properties. In this context, the quantum kagome antiferromagnet ${\mathrm{YCu}}_3{\left(\mathrm{OH}\right)}_6{\mathrm{Cl}}_3$, which has been recently reported as the first geometrically perfect realization of the kagome lattice with negligible magnetic/nonmagnetic intersite mixing and a possible quantum-spin-liquid ground state, is of particular interest. However, contrary to previous conjectures, here we show clear evidence of bulk magnetic ordering in this compound below $T_N=15$ K by combining bulk magnetization and heat capacity measurements, and local-probe muon spin relaxation measurements. The magnetic ordering in this material is rather unconventional in several respects. First, a crossover regime where the ordered state coexists with the paramagnetic state extends down to $T_N/3$ and, second, the fluctuation crossover is shifted far below $T_N$. Moreover, persistent spin dynamics that is observed at temperatures as low as $T/T_N=1/300$ could be a sign of emergent excitations of correlated spin loops or, alternatively, a sign of fragmentation of each magnetic moment into an ordered and a fluctuating part.

• Received 3 April 2019
• Revised 3 June 2019

DOI:https://doi.org/10.1103/PhysRevB.99.214441