Electron spin resonance investigation of the spin-1/2 kagome antiferromagnet ZnCu3(OH)6Cl2

We report a temperature and frequency dependent electron spin resonance (ESR) study of the kagome spin-1/2 compound ZnCu3(OH)6Cl2. Our results demonstrate that two spin species are simultaneously detected; copper spins on the intra-plane Cu2+ kagome sites and those on the inter-plane Zn2+ sites, the latter resulting from the Cu2+/Zn2+ antisite disorder. We examine all the possible magnetic anisotropy terms, which could lead to the observed extremely broad ESR lines in this system. We argue that the line broadening is due to Dzyaloshinsky-Moriya interaction.