Low-temperature dynamic freezing and the fragility of ordering in Tb ₂Sn₂O₇

We have probed the low-temperature magnetic behavior of the ordered spin-ice material Tb₂Sn₂O₇ through ac magnetic susceptibility measurements of both the pure material and samples with small percentages of Ti substituted on the Sn sublattice. We observe a clear signature for the previously reported ordering transition at T_C=850 mK, as well as evidence for dynamic freezing at temperatures well below T_C, confirming the persistence of significant magnetic fluctuations deep in the spin-ordered regime. The long-range-ordering transition was completely suppressed with as little as 5% Ti for Sn substitution, and 10% Ti substitution resulted in a spin-glass-like spin freezing transition near 250 mK. The results demonstrate that the long-range magnetic ordering is surprisingly fragile in this system.