Hysteresis curves and magnetization processes in a model for an amorphous magnet with random uniaxial anisotropy

We consider the magnetic field behavior of a simple model for an amorphous ferromagnet with random single-ion anisotropy. The spins are taken as classical unit vectors located at sites of a dense random packing model and coupled via nearest-neighbor exchange interactions. An easy-axis direction is chosen at random for each site. For large anisotropy, the coercivity is very large and the hysteresis curves resemble those found for amorphous TbFe2 at low temperature. As the anisotropy is reduced, there is a fairly abrupt change in the behavior of the model indicating that sufficiently weak random anisotropy is effectively averaged away. We have examined the energy of metastable states. The results indicate that the canted aligned state is always more stable than low-moment spin-glass-like states. We also consider the magnetization process in the presence of imposed domain walls and find that wall motion is preceeded by magnetization rotation in the high-coercivity regime.