SINGULARITIES IN THE MAGNETIZATION PROCESSES OF HIGH ANISOTROPY MATERIALS

Singularities of various kind are often observed in the magnetization curve of a ferromagnetic crystal. This is especially true for high ani sotropy materials, such as the rare earth - intermetallic compounds. E xamples are the First Order Magnetization Processes (FOMP), which are discontinuous rotations of the magnetization vector due to high order anisotropy terms. However, the hard direction anisotropy field of any ferromagnetic crystal is always a critical field at which it reaches s aturation. The Singular Point Detection (SPD) technique allows detecti ng such singularities using polycrystalline samples by the observation of the successive derivatives d(n)M/dH(n). The shape of the singulari ty and the order of differentiation ''n'' at which it becomes apparent depends on the symmetry of the hard axis. The SPD theory has been rec ently extended to multidomain crystallites on the basis of the Neel ph ase theory, and utilized for texture studies of permanent magnets. Mor eover it has been proved to be valid also in the presence of canting b etween the sublattice moments caused by strong competition between ani sotropy and exchange; in principle, in the case of ferrimagnetic compo unds it is possible to detect spin flop transitions both of second and first order (high FOMP). The application of the SPD approach to the g eneral problem of the complex susceptibility tensor and its covariant derivatives can lead to further developments. As an example, the singu larity observed in the transverse susceptibility of uniaxial materials is strongly sensitive to the presence of single domain crystallites.