Using neutron spectrometry we have investigated the magnon dispersion relation for the ferrimagnetic cubic Laves compound ${\mathrm{Ho}}_{0.88}$${\mathrm{Tb}}_{0.12}$${\mathrm{Fe}}_2$ at room temperature and 12 K. The results are described surprisingly well by a very simple near-neighbor exchange model which includes only iron-iron and iron-rare-earth interactions, crystal field anisotropy, and temperature renormalization that is derived from the sublattice magnetization.

• Received 12 January 1976

DOI:https://doi.org/10.1103/PhysRevLett.36.532