Edward Della Torre, Lawrence H. Bennett, R A. Fry, O A. Ducal
tereffect, that is, decay of magnetization with time at a fixed holding field, is often linear in log-time for a limited time window. The slope at the holding field that maximizes the decay rate, normally near the field that maximizes the irreversible susceptibillity, is often used as a measurement of the long-term stability of permanent magnet media. This paper demonstrates that this measurement alone does not indicate the stability at other fields. It is shown here theoretically, using the Preisach-Arrhenius model, and experimentally that for materials in which there is negligible particle interaction and negligible reversible magnetization, the shape of the thermal aftereffect curve is the same as the ascending major hysteresis curve. For materials meeting these criteria, the ratio of the decay coefficient at one field to another is the same as the ratio of the susceptibilities at those two fields. The paper also discusses the effect of interaction on the decay process. In general, the full identification of the Preisach parameters is necessary and sufficient to estimate the decay rate.