Spin-1/2 kagome compounds: Volborthite vs Herbertsmithite

Two kagome compounds, volborthite Cu3V2O7(OH)2·2H2O and herbertsmithite ZnCu3(OH)6Cl2, are compared in order to derive information about the intrinsic properties of the spin-1/2 kagome antiferromagnet. Observed for volborthite are a broad maximum at T ~ J/4 and a large finite value approached at T = 0 in bulk magnetic susceptibility χbulk as well as local one χlocal from the NMR measurements. These must be the intrinsic properties for the spin-1/2 kagome antiferromagnet, as similar behavior was also reported in χlocal for herbertsmithite [Olariu A et al. 2008 Phys. Rev. Lett., 100 087202]. Impurity effects that may influence seriously the bulk properties are discussed.