HEAT CAPACITY SINGULARITY FOR A FERROMAGNET IN A FINITE APPLIED FIELD

The heat capacity of a ferromagnet in a magnetic field is of value in establishing thermodynamic properties near the Curie point, but certain complications arise due to demagnetizing effects. These should lead, in particular, to a singularity (nonanalytic behavior, not a divergence) in the heat capacity C as a function of temperature when the latter reaches the value where the spontaneous magnetization Ms equals the external field divided by the demagnetizing factor D. If the initial susceptibility χ at this temperature is finite, C decreases by an amount DT(dMs/dT) 2/(1+Dχ). If χ is infinite, C is continuous but will possess a discontinuous slope or other stronger (or weaker) singularity which can be related to the dependence of magnetization on field at fixed temperature. There is no reason (in general) to expect this singularity to be the same as that observed at the critical temperature in zero applied field. © 1969 The American Institute of Physics.