Polarized inelastic neutron scattering of the partially ordered Tb2Sn2O7

We present inelastic neutron scattering results on the geometrically frustrated pyrochlore Tb2Sn2O7. At high temperature T gt;50K, this system resembles the cooperative paramagnet Tb2Ti2O7, while at low temperature T 60mK, it displays remarkably different behavior. Powder neutron scattering, susceptibility and specific heat techniques have shown that below 0.87K Tb2Sn2O7 enters a partially ordered state that is characterized by two sublattice ferrimagnetic long range order which coexists with paramagnetic spin components. We show that i the low temperature state produces a large internal field and collective excitations and ii the coexisting paramagnetic state persists down to 0.1K, with spins fluctuation at a rate greater than 0.04 THz, resulting in a diffuse magnetic background to the diffraction patterns. A low lying excitation at 1.2meV partially softens as short range correlations build up while cooling in the paramagnetic stat