Spin Dynamics of the S = 1/2 Pyrochlore System Cu_2(OH)_3Cl Studied by Using High-frequency ESR

Spin Dynamics of the S = 1/2 Pyrochlore System Cu_2(OH)_3Cl Studied by Using High-frequency ESR

We report a magnetization and electron spin resonance (ESR) study of the clinoatacamite Cu_2(OH)_3Cl, 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 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 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 kagomé lattice in Cu_3Zn(OH)_6Cl_2 [Zorko et al., Phys. Rev. Lett. 101, 02640 (2008)]. This suggests that the magnetic properties of Cu_2(OH)_3Cl may be described in terms of a stack of kagomé lattices.

We report a magnetization and electron spin resonance (ESR) study of the clinoatacamite Cu_2(OH)_3Cl, 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 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 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 kagomé lattice in Cu_3Zn(OH)_6Cl_2 [Zorko et al., Phys. Rev. Lett. 101, 02640 (2008)]. This suggests that the magnetic properties of Cu_2(OH)_3Cl may be described in terms of a stack of kagomé lattices.