Experimental Determination of the Critical Spin Glass Correlation Length

Measuring ThermoRemanent Magnetization (TRM) decays on a single crystal CuMn(6$%$) spin glass sample, we have systematically mapped the rapid decrease of the characteristic timescale $tw_{eff}$ near $T_g$. Using $tw_{eff}$ to determine the length scale of the growth of correlations during the waiting time, $xi_{TRM}$, (observed in both numerical studies and experiment), we observe both growth of $xi_{TRM}$ in the spin glass phase and then a rapid reduction very close to $T_g$. We interpret this reduction in $xi_{TRM}$, for all waiting times, as being governed by the critical correlation length scale $xi_{crit}=a(T-T_c)^{- u}$.