Calorimetric studies of magnetic hysteresis in CuMn alloys

Calorimetric measurements on the hysteresis loop of the spin glass CuMn show that the energy changes take place on those legs of the loop which correspond to reversals of the remanent magnetisation and that it is always heating which occurs, irrespective of the direction of the applied magnetic field. Cycling through successive hysteresis loops causes large initial changes in sample heating and loop area, with both of these quantities tending to a temperature-independent limit. Although the limit cycle is displaced from the origin, the thermal energy changes on both irreversible legs are approximately equal, indicating a change of internal magnetic energy on reversal of the remanence. It is argued that the energy released in the initial magnetisation reversals is attributable to irreversible rearrangements of the relative spin directions and that it is only in the limit cycle that energy changes represent exclusively the intrinsic irreversible processes of magnetisation reversal.