Aging, rejuvenation, and memory effects in Ising and Heisenberg spin glasses - art. no. 174204

We have compared aging phenomena in the Fe0.5Mn0.5TiO3 Ising spin glass and in the CdCr1.7In0.3S4 Heisenberg-like spin glass by means of low-frequency ac susceptibility measurements. At constant temperature, aging obeys the s ame "wt scaling" in both samples as in other systems, Investigating the eff ect of temperature variations, we find that the Ising sample exhibits rejuv enation and memory effects which are qualitatively similar to those found i n other spin glasses, indicating that the existence of these phenomena does not depend on the dimensionality of the spins. However, systematic tempera ture cycling experiments on both samples show important quantitative differ ences. In the Ising sample, the contribution of aging at low temperature to aging at a slightly higher temperature is much larger than expected from t hermal slowing down. This is at variance with the behavior observed until n ow in other spin glasses, which show the opposite trend of a free-energy ba rrier growth as the temperature is decreased. We discuss these results in t erms of a strongly renormalized microscopic attempt time for thermal activa tion and estimate the corresponding values of the barrier exponent psi intr oduced in the scaling theories.