Aging in a topological spin glass

We have examined the nonconventional spin glass phase of the 2-dimensional kagome antiferromagnet (H_3 O) Fe_3 (SO_4)_2 (OH)_6 by means of ac and dc magnetic measurements. The frequency dependence of the ac susceptibility peak is characteristic of a critical slowing down at Tg ~ 18K. At fixed temperature below Tg, aging effects are found which obey the same scaling law as in spin glasses or polymers. However, in clear contrast with conventional spin glasses, aging is remarkably insensitive to temperature changes. This particular type of dynamics is discussed in relation with theoretical predictions for highly frustrated non-disordered systems.