Coexistence of magnetic order and persistent spin dynamics in a quantum kagome antiferromagnet with no intersite mixing

Abstract

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 ${\mathrm{YCu}}_{3}{(\mathrm{OH})}_{6}{\mathrm{Cl}}_{3}$, 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.