Spin glassiness and power law scaling in anisotropic triangular spin-1/2 antiferromagnets

We present data on the magnetic properties of two classes of layered spin S=1/2 antiferromagnetic quasi-triangular lattice materials: Cu2(1?x)Zn2x(OH)3NO3(0?x?0.65) and its long-organic-chain?intercalated derivatives Cu2(1?x)Zn2x(OH)3(C7H15COO)?mH2O(0?x?0.29), where non-magnetic Zn substitutes for Cu isostructurally. It is found that the intercalated compounds, even in a clean system in the absence of dilution, x=0, show spin glass behaviour, as evidenced by DC and AC susceptibility, and by time-dependent magnetization measurements. A striking feature is the observation of a sharp crossover between two successive power law regimes in the DC susceptibility above the freezing temperature. In constrast to standard theoretical expectations, these power laws are insensitive to doping. Specific heat data are consistent with a conventional phase transition in the unintercalated compounds, and glassy behaviour in the intercalated compounds.