Dynamics in pure and substituted volborthite kagome-like compounds

Volborthite Cu3V2O7(OH)2·2H2OCu3V2O7(OH)2·2H2O is a natural frustrated antiferromagnet with a kagomé-like magnetic lattice decorated by S=12 spins. Our μμSR results confirm the existence of a dynamical plateau below 2 K, as initially demonstrated in [Phys. Rev. Lett. 91 (2003) 207603] despite sensible quantitative differences in the relaxation rate values. Thanks to additional low temperature SQUID and NMR data we show that this plateau occurs concurrently with a freezing transition. Moreover, we revisited the effect of diluting the magnetic lattice for small dilution rates between 1% and 15%. Comparison is made with the well studied kagomé bilayer compounds. The ground state of volborthite appears to be far less stable with respect to dilution.