Magnetic susceptibility of the kagome antiferromagnet ZnCu3(OH)6Cl2

We analyze the experimental data for the magnetic susceptibility of the material ZnCu3(OH)6Cl2 in terms of the Kagome Lattice Heisenberg model (KLHM), discussing possible role of impurity spins, dilution, exchange anisotropy, and both out-of-plane and in-plane Dzyloshinski-Moriya (DM) anisotropies, with explicit theoretical calculations using the numerical linked cluster method and exact diagonalization. The high-temperature experimental data are well described by the pure Heisenberg model with J=170K. We show that the sudden upturn in the susceptibility around T=75K is due to DM interactions. We also observe that at intermediate temperatures, below T=J, our calculated susceptibility for KLHM fits well with a power law T-0.25.