Theory of the spin dynamics of paramagnetic EuO and EuS

The method of moments is used to investigate the dynamics of paramagnetic EuO and EuS. The theory predicts correctly those wavevectors for which a 'spin wave' peak appears in the spectrum. Furthermore the calculated position of this peak, when one occurs, agrees well with experiment. This suggests that earlier work, in which the same method was applied to an effective Heisenberg model for Fe, was correct in predicting that this model has no 'spin wave' peaks in the wavevector range covered experimentally