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 Cu-2(OH)(3)Cl, which is known to have a S = 1/2 distorted pyrochlore lattice. The static magnetic susceptibility shows a strong increase at temperatures below T-N2 = 6.4 K without any appreciable anomalies at T-N1 = 18.1 K. The magnetization vs. field curve exhibits the presence of a weak ferromagnetic moment of 0.1 mu(B)/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 similar to 170 K. The temperature dependence of the linewidth is characterized by three distinct temperature regions: (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 kagome lattice in Cu3Zn(OH)(6)Cl-2 [Zorko et al.; Phys. Rev. Lett. 101, 02640 (2008)]. This suggests that the magnetic properties of Cu-2(OH)(3)Cl may be described in terms of a stack of kagome lattices.