Low-T dynamics in the highly frustrated kagomé bilayers: A phenomenological function for a spin liquid state?

A muSR study of the spin dynamics of the archetypes of the highly frustrated magnets, SrCr9pGa12-9pO19 and Ba2Sn2ZnGa10-7pCr7pO22, is summarized. Especially, low dilutions of the magnetic network could be achieved and we take advantage of the close similarity between these kagome bilayers to single out their typical properties. The phenomenological model for the mu+ relaxation, based on sporadic dynamics due to spin excitations in a singlet sea, proposed by Uemura et al., is extended to all fields, temperature and defects range. Its connection to a RVB picture is discussed.