Specific heat and magnetic ordering of ErBi studied with crystal-field theory in the mean-field approach

The low-temperature specific heat of ErBi is evaluated quantitatively with crystal-field (CF) theory in the mean-field approach by using a set of crystal-field parameters (CFPs) proposed by previous authors. The calculated temperature dependence of the heat capacity exhibits a sharp peak at the magnetic-transition temperature, and shows good agreement with the experimental results over the whole temperature region. To further investigate the mechanism of the magnetic ordering of the material, we have calculated the spontaneous magnetization for the case that only the ground-state CF level is considered and also for the case that the two lowest CF levels are considered, to compare with the results obtained with the full set of CF states of the J=152 multiplet. The results suggest that the two lowest CF levels play a dominant role in the magnetic ordering below TN.