Magnetization processes in barium ferrite micropowders.

The magnetization processes in barium ferrite micro-powders subjected to various annealing and milling treatments were investigated by the methods of magnetic analysis. The anisotropy field distributions were found to vary with the coercive force, being dependent on the dislocation density. The samples with the lower values of the coercive force had more particles in the low-anisotropy-field region than the samples with the higher coercive forces. Wohlfarth's remanence relationships are not obeyed, the discrepancies being attributed to the presence of domains. A particular type of domain structure, the cylindrical domain, was postulated to explain an asymmetrical magnetization process occurring. The discrepancies from Wohlfarth's relationships and the extent of the asymmetry are related to the dislocation density in a manner similar to that used to explain the anisotropy field distribution results. The role of dislocations in reducing the anisotropy and in acting as domain-wall nucleation centres was considered and justified by a brief theoretical account of the possible dislocations in barium ferrite