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

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 YCu3(OH)6Cl3, 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 TN = 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 TN/3 and, second, the fluctuation crossover is shifted far below TN. Moreover, persistent spin dynamics that is observed at temperatures as low as T/TN = 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.

近年来，受挫晶格（frustrated lattices）领域涌现的核心问题之一，是无序在诱导类自旋液体特性中所起的作用。在此背景下，近期被报道为首个几何上完美实现笼目晶格（kagome lattice）、磁/非磁位点间混合可忽略不计、且可能存在量子自旋液体基态的量子笼目反铁磁体YCu₃(OH)₆Cl₃，具有格外重要的研究价值。然而与此前的推测相悖，本文结合体相磁化强度、热容量测量以及局域探针μ子自旋弛豫（muon spin relaxation）测量，为该化合物在T_N=15 K以下存在体相磁有序提供了明确的实验证据。该材料中的磁有序在多个方面均表现出非寻常特性：其一，有序态与顺磁态共存的交叉区域可延伸至T_N/3处；其二，涨落交叉点远低于T_N。此外，在低至T/T_N=1/300的温度下仍可观测到持续自旋动力学现象，这一现象既可能是关联自旋环的涌现激发信号，也可能代表每个磁矩被分裂为有序部分与涨落部分的特征。