Dilution in volborthiteS= 1/2 frustrated magnet: a SR and NMR study

Volborthite, Cu 3 V 2 O 7 (OH) 2 ·2H 2 O, is a natural frustrated antiferromagnet ( K) with S = 1/2 spins (Cu 2+ ) sitting at the vertices of a Kagomé-like lattice built on isosceles triangles. We report on the static (SQUID, 51 V NMR) magnetic properties of the pure and 5% Zn/Cu substituted compounds and on an extensive μSR study of the dilution effect (up to 15% Zn substitutions) on the spin dynamics. Although volborthite shares most of the unusual features already exhibited in Kagomé bilayer compounds, namely a dynamical state as and a low temperature maximum in the local susceptibility, we found some surprising specificities. The dynamical state is less robust against dilution and the low temperature local susceptibility studied by means of NMR also strongly depends on dilution. Such a sensitivity to dilution questions the role of the asymmetry of the exchange constants.