A dynamic probe of finite-size effects near the spin-glass transition temperature*

Using a high sensitivity dual DC SQUID magnetometer, we have measured the growth of the spin glass correlation length, through the aging and end of aging effects. Measurements were made on bulk CuMn5% and a CuMn12% thin film multilayer with CuMn layer thicknesses of 4.5 nm. As the glass temperature Tg is approached (0.9Tg < T<0.96Tg) in the bulk sample, we find that the waiting time effect (as measured by the time associated with the inflection point of the decay) as a function of increasing temperature, shifts to shorter timescales. For T >0.96Tg, there is no waiting time effect (end of aging) on the magnetization decay. and all decays collapse onto a single decay curve indicating an end of aging even for long waiting times (tw = 10,000s). For the thin film, all effects due to the waiting time disappear at around 0.89T_f, where T_f is the freezing temperature marking the onset of irreversibility. The end of aging results are interpreted in terms of the spin glass correlation length saturating due to finite size effects.