Finite Size Effects on Spin Glass Dynamics

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The recent identification of a time and temperature dependent spin glass correlation length, ξ(tw,T), has consequences for samples of finite size. Qualitative arguments are given on this basis for departures from t/tw scaling for the time decay of the thermoremanent magnetization, MTRM(t,tw,T), where t is the measurement time after a ``waiting time'' tw, and for the imaginary part of the ac susceptibility, χ′′(ω,t). Consistency is obtained for a more rapid decay of MTRM(t,tw,T) with increasing tw when plotted as a function of t/tw, for the deviation of the characteristic time for MTRM(t,tw,T) from a linear dependence upon H² at larger values of H, and for the deviation of the decay of χ′′(ω,t) from ωt scaling upon a change in magnetic field at large values of ωt. These departures from scaling can, in principle, be used to extract the particle size distribution for a given spin glass sample.