The Specific Heat Discontinuity in Antiferromagnets and Ferrites

It is shown that, in a molecular field approximation, the internal energy and specific heat of a ferromagnet and antiferromagnet have the same form, regardless of the number of sets of neighbors whose interactions are considered and of the signs of the interactions. The Néel theory is used to derive an expression for the discontinuity in specific heat in ferrites at the Curie temperature. This discontinuity $\Delta C$ is in general smaller than it would be for a ferromagnet or antiferromagnet with the same number of atoms. Numerical calculations indicate that for most ferrites $\Delta C$ should decrease monotonically as nonmagnetic atoms are substituted for magnetic atoms on the $A$ sites. On the other hand, if the nonmagnetic atoms go on the $B$ sites, $\Delta C$ should pass through a maximum.