The low-temperature properties, in iron garnets, of rare-earth ions with an odd number of electrons can be described by a simple model. This model represents the energy levels of the rare-earth ion by an isolated doublet which is subjected to an anisotropic exchange interaction. The complex shapes of the torque curves, predicted by the model and observed at low temperature, are represented by Fourier expansions. A small torque contribution proportional to the applied magnetic field is predicted, and evidence of its existence is observed in (YbY) and (YbGd) iron garnets. A comparison of the behavior of Yb and Dy in YIG and GdIG indicates a moderate influence of the host lattice on Yb and a drastic influence on Dy. The anisotropy anomaly observed for Yb in YIG [at 32°from  in the (110) plane] is not present when Yb is substituted into GdIG. © 1962 The American Institute of Physics.