Aging, rejuvenation, and memory effects in Ising and Heisenberg spin glasses

Abstract

We have compared aging phenomena in the Fe 0.5 Mn 0.5 TiO 3 Ising spin glass and in the CdCr 1.7 In 0.3 S 4 Heisenberg-like spin glass by means of low-frequency ac susceptibility measurements. At constant temperature, aging obeys the same ''t scaling'' in both samples as in other systems. Investigating the effect of temperature variations, we find that the Ising sample exhibits rejuvenation and memory effects which are qualitatively similar to those found in other spin glasses, indicating that the existence of these phenomena does not depend on the dimensionality of the spins. However, systematic temperature cycling experiments on both samples show important quantitative differences. In the Ising sample, the contribution of aging at low temperature to aging at a slightly higher temperature is much larger than expected from thermal slowing down. This is at variance with the behavior observed until now in other spin glasses, which show the opposite trend of a free-energy barrier growth as the temperature is decreased. We discuss these results in terms of a strongly renormalized microscopic attempt time for thermal activation and estimate the corresponding values of the barrier exponent introduced in the scaling theories.

Spatially heterogeneous ages in glassy systems

“…30 these values change quite a bit if one uses instead a fitting procedure with the Yukawa form in Eq. (68). As mentioned before, the simple exponential form provides a better fit for the range of distances accessible in our simulations.…”

“…Note that this "2-point correlator" differs from ours in that (i) it is evaluated at equal times, (ii) there is a further average over the noise, and, more importantly, (iii) the two-point functions that one further correlates are evaluated between two copies of the system evolving independently. The latter property implies that this length can only be tested experimentally with indirect measurements [23,68]. Interesting enough, the length we define in this paper is, in principle, accessible directly with local experimental probes.…”

Memory effect and spin-glass-like behavior in Co-Ag granular films

“…We focused on the study of memory effect because it is usually considered as typical characteristics of the spinglass dynamics and has been clearly observed in different ͑canonical͒ spin-glass systems. [25][26][27] Although the spin-glass state was found in Fe-Cu ͑Ref. 28͒ and Co-Cu ͑Ref.…”

Experimental investigation of the fluctuation dissipation relation in a spin glass

“…10 Despite its esoteric nature, this concept was a very powerful qualitative tool, making understandable most of the far from intuitive manifestations of non-stationarity in spin glasses, what is known now as "rejuvenation" and "memory" effects. 11 …”