Activated dynamic scaling in spin glasses above the freezing temperature

Dynamic-susceptibility data on Eu0.4Sr0.6S spin glass above its transition temperature are found to obey an activated (logarithmic) dynamic scaling form, implying a generalized Vogel-Fulcher relation exp[c(T-Tg)] with 0.65. With use of a fractal-cluster model, a novel scaling relation for another of the exponents is derived and tested experimentally. The "2 rule" relating real and imaginary susceptibilities is derived for systems obeying activated scaling. © 1986 The American Physical Society.