The heat capacity is one of the few bulk physical properties amenable to theoretical modeling. The measured C_p can be represented as the sum of various contributions depending upon the nature of the material under study. With data of an appropriate quality, one can obtain excellent fits of the theoretical models for these contributions. Our on-going work on single CoO illustrates this nicely. CoO is an interesting material because it has a magnetic transition at a temperature that is comparable to the temperatures needed to cause thermal excitation to excited crystal field states. Most magnetic materials order at temperatures that are much lower than the temperatures at which their excited electronic states become populated. The heat capacity of CoO can be considered to be a sum of three terms, the contributions from the lattice vibrations, the magnetic transition, and the electronic excitations. Getting at the magnetic contribution to the heat capacity is complicated by the need to eliminate the electronic (Schottky) contribution from the measured heat capacity as well as those of the lattice. The contributions of the lattice vibrations and the electronic excitations can be modeled if the vibrational and electronic energy levels are known from spectroscopic studies. The results of one attempt at such a modeling are shown in the figure below on the left, where the various contributions to C_pare shown. To the right is the estimation of the magnetic contribution to the heat capacity. Because this estimation gives a magnetic entropy that is significantly higher than expected, we are trying other methods to estimate the lattice heat capacity, since this is the most likely culprit for the source of error.

Resolution Of The Experimental Heat Capacity Of Single Crystal CoO Into Its Components

Magnetic Heat Capacity in Single Crystal CoO