Specific Heat of EuO

We report measurements of the specific heat C of two single crystals of EuO over the range of temperatures from 0.37° to 4.4°K and in the presence of external magnetic fields up to 13 kOe. The results for these two samples, which were grown from different batches, are consistent within a few percent. The primary contribution to C above 0.7°K is described in terms of spin-wave theory. From an analysis of the data we find J1/kB=(0.76±0.02) °K and J2/J1=−0.11±0.02 in excellent agreement with another determination. Below 0.7°K, the dominant contribution to C arises from the hyperfine splitting of the 151Eu and 153Eu nuclear levels. The magnitude of this contribution corresponds to an effective hyperfine field HN=300±5 kOe in agreement with the value deduced from NMR and Mössbauer experiments.