Dynamic frustrated magnetism inTb2Ti2O7at 50 mK

The low temperature $(T<\mathrm{}1\mathrm{}\mathrm{K})$ properties of the cooperative paramagnet ${\mathrm{Tb}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ have been studied by ac susceptibility, neutron diffraction and neutron spin echo techniques. Like several other frustrated magnets, ${\mathrm{Tb}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7,$ is believed to remain paramagnetic down to $\sim 0.07\mathrm{K}.$ However, recent studies [Yasui et al., J. Phys. Soc. Jpn. 71, 599 (2002), for example] suggest that ${\mathrm{Tb}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ enters an ordered, albeit glassy, state at a relatively high temperature, $\sim 1.5\mathrm{K}.$ Our results confirm that the majority of the spins in ${\mathrm{Tb}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ 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.