Interdependence of thermal aftereffect and natural aging in permanent magnet materials

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.