Quantum magnetism in the paratacamite family: towards an ideal kagome   lattice
  We report MuSR measurements on the S=1/2 (Cu2+) paratacamite Zn_xCu_{4-x}(OH)_6Cl_2 family. Despite a Weiss temperature of -300 K, the x=1 compound is found to have no transition to a magnetic frozen state down to 50 mK as theoretically expected for the kagome Heisenberg antiferromagnet. We find that the limit between a dynamical and a frozen inhomogeneous ground state occurs around x=0.5. For x=1, we discuss the relevance to a singlet picture. 
P. Mendels, F. Bert, M.A. de Vries, A. Olariu, A. Harrison, F. Duc,   J.C. Trombe, J. Lord, A. Amato, C. Baines