Neutron scattering studies on Kagome bilayers -- Spin fluctuations in a broad dynamic range

The kagome bilayer compounds Ba2Sn2ZnCr7xGa10-7xO22 and SrCr9xGa12-9xO19 are localized spin (S=3/2) systems with strong antiferromagnetic exchange (J/k $\approx $ 50 K) that show no long-range order down to mK temperatures. This remarkable behaviour originates from the geometrical frustration. We have examined these systems using polarized neutron diffraction, inelastic neutron scattering (INS) and neutron spin-echo (NSE) spectroscopy for characterizing the magnetic correlations in a very broad energy range. INS data reveals the dynamic nature of the broad diffuse scattering that characterises the quasi-elastic magnetic response above the spin freezing. New aspects on the freezing phenomenon and the ground state properties are revealed using NSE.