Activated dynamic scaling in spin glasses above the freezing temperature

Dynamic-susceptibility data on Eu0.4{Sr}0.6$S spin glass above its transition temperature are found to obey an activated (logarithmic) dynamic scaling form, implying a generalized Vogel-Fulcher relation ${τ}{∝}exp[{c}{{(T{-}{T}g)}^{{ν}{θ}}}]$ with ${ν}{θ}{~}0.65$. With use of a fractal-cluster model, a novel scaling relation for another of the exponents is derived and tested experimentally. The "${{π}}{2}$ rule" relating real and imaginary susceptibilities is derived for systems obeying activated scaling.