Interdependence of thermal aftereffect and natural aging in permanent magnet materials

Abstract

The thermal aftereffect is proportional to the irreversible susceptibility \chi irr and thus has a peak value in the zone of coercive force. It follows a logarithmic time law of the type \Delta I= S \cdot \log t + const whose constant S shows a linear increase with the absolute temperature T . The quotient S/\chi irr is a material constant and proportional to the coercive force. Natural aging also follows a law of the form \Delta B = S \cdot \log t + const , but is not proportional to \chi irr and therefore does not have a peak value in the zone of coercive force. Natural aging disappears at the remanence and at the coercive force. The constant S of natural aging is proportional to the product I \cdot H \cdot \chi irr and inversely proportional to the coercive force. The quotient S/\chi irr is, in this case, not a material constant and not proportional to the coercive force.