Experimental Determination of the Critical Spin Glass Correlation Length*

We have made detailed measurements of the waiting time effect of the thermoremanent magnetization (TRM) near the spin glass transition temperature T_g. In previous measurements we found that the timescale t_weff associated with the decay, rapidly decreases near T_g (where T_g is defined by the onset of remanence). This effect has been systematically mapped out for waiting times ranging from 300 s to 100,000 s. Using t_weff to determine the length scale of the glassy correlations, ξ_glassy, (observed in both numerical studies and experiment) we see both growth of this correlation length as T_g is approached (from lower temperatures), and then a rapid reduction of this correlation length very close to T_g. We interpret this reduction in ξ_glassy, for all waiting times, as being governed by the critical correlation length ξ_crit . The data from all waiting times collapse on a master curve that can be fit to (T-T_c)^-zn.