Micromagnetics of magnetization processes in toroidal geometries

The micromagnetics of competition between magnetostatic and exchange energies is investigated for two geometries. For a cylindrical tube an approximate solution yields the magnetization for all values of the applied magnetic field producing remanence, a coercive field and a critical field at which the magnetization changes irreversibly. The behavior in the irreversible region is also calculated. For the geometry of a thin toroidal shell it is found that most of the reversal processes is divergentless, but in a crucial region magnetic charges develop.