THERMAL-DIFFUSION DISPERSION IN DISORDERED-SYSTEMS

A thermal diffusion process is discussed, that should be expected in a ny system in which the difference in the local susceptibilities chi(T) - chi(S) is inhomogeneous, where the superscripts indicate isothermal and adiabatic processes. That constitutes an universal secondary resp onse of disordered systems which must be considered in conjunction wit h the primary ''mechanical'' response. The response function due to th ermal diffusion behaves asymptotically as e(-(t/tau)1/2) for short tim es and as t(-3/2) for long times, but can be interpolated by e(-(t/T)0 .60) for a wide range of times around T. The thermal diffusion process can be particularly relevant in the response of magnetic glasses, ele ctric dipole glasses, and in multidomain ferroelectric/ferromagnetic s ystems with more than two domain orientations.