Dynamics in pure and substituted volborthite kagome-like compounds

Abstract : Volborthite Cu 3 V 2 O 7 ðOHÞ 2 Á 2H 2 O is a natural frustrated antiferromagnet with a kagome´-kagome´-like magnetic lattice decorated by S ¼ 1 2 spins. Our mSR 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 kagome´bilayerkagome´bilayer compounds. The ground state of volborthite appears to be far less stable with respect to dilution.