We propose a new model for magnetism in an amorphous material. The model is particularly appropriate for rare-earth compounds such as Tb${\mathrm{F}}_2$. It is a Heisenberg model in which each ionic spin is subjected to a local anisotropy field of random orientation. We discuss the magnetic properties of two simple ionic configurations, and show that the model is in qualitative agreement with the experimental data.

• Received 9 April 1973

DOI:https://doi.org/10.1103/PhysRevLett.31.160