Dynamical susceptibility of spin glasses in the fractal cluster model

We study the dynamical susceptibility of spin glasses above the critical temperature using a fractal cluster model. We derive scaling relations for the zero-field limit of the real and imaginary parts of which are general since they do not depend on a particular relaxation model. Comparison to data on Eu0.4Sr0.6S yields critical exponents in good agreement with independent determinations. We discuss the different criteria which have been used to extract the critical relaxation time from experimental 's. The smallness of the ratio z between critical exponents in the spin-glass problem justifies the approximations used to interpret and relate experimental data, for example, with the equation =-d2dln. © 1986 The American Physical Society.