HYSTERESIS AND AFTEREFFECTS IN MASSIVE SUBSTANCES - FROM SPIN-GLASSES TO THE SAND HILL

The author discusses the problem of magnetic hysteresis in the framework of a model of a distribution of thermally activated double well potentials. Having shown the equivalence, at T equals O, of this description with classical picture of Preisach and Neel the effects associated with the fact that the width of the distribution of the barrier-heights is necessarily finite are considered specifically, showing how this limit can be introduced in the classical Preisach construction and how it opens the door to the decription of after-effects (in terms of time and of temperature) as well as to the description of the effect of the field beyond the Rayleigh domain. A justification of the Preisach construction is attempted within a language more adapted to the great generality of this construction which successfully applies to magnetic as well as to mechanical hysteresis or to the weight of a sand hill ! ! . . . This could be viewed as a first-order approach of non ergodic problems.