Spin dynamics and magnetic order in magnetically frustrated Tb2Sn2O7
  We report a study of the geometrically frustrated magnetic material Tb2Sn2O7 by the positive muon spin relaxation technique. No signature of a static magnetically ordered state is detected while neutron magnetic reflections are observed in agreement with a published report. This is explained by the dynamical nature of the ground state of Tb2Sn2O7: the Tb3+ magnetic moment characteristic fluctuation time is ~ 10^{-10} s. The strong effect of the magnetic field on the muon spin-lattice relaxation rate at low fields indicates a large field-induced increase of the magnetic density of states of the collective excitations at low energy. 
P. Dalmas de Reotier, A. Yaouanc, L. Keller, A. Cervellino, B.   Roessli, C. Baines, A. Forget, C. Vaju, P.C.M. Gubbens, A. ...