The decay of the thermoremmnent magnetization of a reentrant CoyF4, ferromagnet with 7, 2' 70 K has been mezured as a function of temperature T and wait time I,. over an observation time interval I s c f c IO'S. A characteristic temperature T, 2 25 K is identified, below which the relaxation dynamics show the non-equilibrium age dependence and thermal cycling effects typical of glassy materials. and above which the dynamics we 'stationary'. Fits to the predictions of a model based on anomalous diffusion among random free energy Iraps.with lifetimes r distributed according to $ f r )r-(""'. show that the dynamic crossover is consistent with a change in the structure of phase space. from a regime T c T, where x c I, ergodicity is broken for 311 finite system ages. and the system configurations resemble those of the random energy model. to a regime T > T, where x > I. and the system ergodically probes every available trap. resulting in a unique relaxation response. This analysis provides a quantitative link between 'reentrmcy' and the formation of a glssy spin structure below Te as well as suppon for a particular aging mechanism of genenl applicability to all disordered systems.

We demonstrate how spatial cross-correlation image analysis can be used to characterize the strain rate dependence of simulated plastic damage for three systems, two copper bi-crystals containing complementary tilt grain boundaries, and a copper crystal without a grain boundary strained along the [011] direction. Distributions of cross-correlation coefficients (CCs) generated within the same system and strain rate are used to characterize the range of different types of damage observed, while CC distributions generated between the same system but at different strain rates indicate the degree of similarity of the damage generated between strain rates. For both bi-crystals, the CC distributions indicate a broader range of damage configurations as strain rate decreased. For a 15° tilt angle CC distributions generated between the damage configurations at the highest and the lowest strain rates indicate a common set of damage configurations, while for the 45° tilt angle the same analysis suggested comparatively fewer similar damage configurations. In contrast, lower strain rates for the system without initial grain boundaries resulted in far fewer distinct damage configurations and a high degree of matching between the similar configurations. In this case the damage is composed of ordered stacking faults along the (111) planes.