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 ∼0.07 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, ∼1.5 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.