Extraction of the spin glass correlation length

The peak of the spin glass relaxation rate, S(t) = d[-M-TRM(t,t(w))/H]/d ln t, is directly related to the typical value of the free energy barrier which can he explored over experimental time scales. A change in magnetic field H generates an energy E-z = N(s)chi(fc)H(2) by which the barrier heights are reduced, where chi(fc) is the field cooled susceptibility per spin, and N-s is the number of correlated spins. The shift of the peak of S(t) gives E-z generating the correlation length, xi(t, T) for Cu:Mn at.% and CdCr1.7In0.3S4. Fits to power law dynamics, xi(t, T) infinity t(a(T)) and activated dynamics xi(t, T) infinity (In t)(1/psi) compare well with simulation fits but possess too small a prefactor for activated dynamics.