Spin dynamics of the S = 1/2 pyrochlore system Cu₂(OH)₃CL studied by using high-frequency ESR

We report a magnetization and electron spin resonance (ESR) study of the clinoatacamite Cu₂(OH)₃Cl, which is known to have a S = 1/2 distorted pyrochlore lattice. The static agnetic susceptibility shows a strong increase at temperatures below TN2 = 6.4 K without any appreciable anomalies at TN1 = 18.1 K. The magnetization vs. field curve exhibits the presence of a weak ferromagnetic moment of 0.1 μB/Cu at T = 2 K, possibly due to an antisymmetric Dzyaloshinsky-Moriya (DM) interaction and/or weak ferromagnetic interplane interactions. From the ESR linewidth, we estimate the magnitude of the DM interaction as 10% of the leading isotropic exchange interaction, J ~170 K. The temperature dependence of the linewidth is characterized by three distinct temperatureregions: (i) a high-temperature exchange narrowing region at temperatures above 170 K, (ii) a two-dimensional short-range ordered region at temperatures between 170 K and 36 K, and (iii) a low-temperature region at temperatures below 36 K where an antiferromagnetic-like resonance mode develops. The evolution of the ESR linewidth is comparable to that of the S = 1/2 kagoḿe lattice in ₃Zn(OH)₆Cl₂ [Zorko et al., Phys. Rev. Lett. 101, 02640 (2008)]. This suggests that the magnetic properties of Cu₂(OH)₃Cl may be described in terms of a stack of kagoḿe lattices.