Dynamic frustrated magnetism in Tb2Ti2O7 at 50 mK

The low temperature (T<1 K) properties of the cooperative paramagnet Tb2Ti2O7 have been studied by ac susceptibility, neutron diffraction and neutron spin echo techniques. Like several other frustrated magnets, Tb2Ti2O7, is believed to remain paramagnetic down to similar to0.07 K. However, recent studies [Yasui et al., J. Phys. Soc. Jpn. 71, 599 (2002), for example] suggest that Tb2Ti2O7 enters an ordered, albeit glassy, state at a relatively high temperature, similar to1.5 K. Our results confirm that the majority of the spins in Tb2Ti2O7 fluctuate very rapidly, even at 50 mK and that static, spatial correlations do not develop beyond nearest neighbor at similar temperatures. We suggest that the observation of a partial freezing of this magnetic system, at finite temperature, is a result of a small fraction of spins freezing around defects in the stoichiometric crystal structure.