Spin dynamics in frustrated magnets: from edge- to corner-sharing geometries

Our work in the past few years has been focused on local NMR ( nuclear magnetic resonance) and mu SR (muon spin resonance) studies of pure Heisenberg isotropic triangular lattices with nearest neighbour couplings, a prerequisite for reaching the ideal spin liquid case. In the case of chromates, although S = 3/2, the combination of the weakness of the Cr3+ single-ion anisotropy and that of an exchange interaction resulting from a direct overlap of the Cr3+ orbitals allows us to tackle these properties. We were recently able to single out, in the triangular compound NaCrO2, an original dynamical crossover regime in a broad range of T between the peak in specific heat and a low T static ground state. Moving to the corner-sharing geometry of Kagome bilayers (Ba2Sn2ZnGa10-7pCr7pO22 and SrCr9pGa12-9pO19), we illustrate all the potential of local studies ( NMR and mu SR) for revealing some key aspects of the physics of these compounds, namely T -> 0 fluctuations, susceptibility, the impact of dilution defects which generate an extended response of the spin lattice as well as their puzzling spin glass state. These results are compared to the case of volborthite which features S = 1/2 spins on a corner-sharing, probably anisotropic, antiferromagnetic Kagome lattice.