Magnon Contribution to the Low‐Temperature Specific Heat of UO₂

The contribution of acoustical phonons to the low‐temperature specific heat of UO₂, as calculated from the single crystal elastic constants, is much too small to account for the observed heat capacity. It is shown here that this data can however be explained in terms of antiferromagnetic magnons. An expression for the heat capacity due to spin waves is derived, firstly for a simple antiferromagnet having a spherically symmetric dispersion relation, and secondly for UO₂, where the dispersion relation is cylindrically symmetrie. For UO₂ it is found that the next nearest neighbour interactions must be included in order to obtain a meaningful dispersion relation.