Search

The effects of quencher after calcination on the microstructure and magnetic properties of manganese-zinc ferrites were investigated by measuring the magnetic properties, electrical resistivity and density. The powder of Mn 0.68 Zn 0.25 Fe 2.07 O 4 composition was prepared by adopting the conventional ceramic technique. Toroidal cores were sintered at 1350 °C for 4 h in atmosphere controlled by using the equation for equilibrium oxygen partial pressure. The fracture surface micrographs of samples were observed by scanning electron microscope. The results show that the inner stress of calcined powder increases, abnormal grains of ferrite grow up, initial permeability goes down and power losses of ferrite rise with the increase in quenching temperature, and the microstructure and magnetic properties of manganese-zinc ferrites can be improved with the gradual cooling of calcined powder to room temperature (25 °C).

The migration process of Co ions in cobalt-ferrite epitaxial layers on γ-Fe2O3 powders has been studied by a magnetic thermal annealing method. The activation energy E and coefficient A of Co ions have been measured. An abnormal increase of coercivity of a sample annealed in a transverse magnetic field was found. On the basis of Mossbauer, XPS and magnetic torque results, the reason for this phenomenon is discussed. The abnormal phenomenon can be interpreted by allowing for a difference of crystalline anisotropy constants corresponding to the samples with and without magnetic thermal annealing in the transverse magnetic field.

The causes of the increased coercivity of cobalt—ferrite epitaxial γ-Fe 2 O 3 were studied. The results show that the coercivity of this powder may be contributed by three kinds of anisotropies: (1) shape anisotropy, (2) crystalline anisotropy and (3) magnetic induced anisotropy of the cobalt—ferrite epitaxial layer of this powder. With magnetic annealing experiments and the method of calculated coercivity of mixed powder, the coercivity contributed by crystalline and magnetic induced anisotropy can be estimated. The calculated coercivity corresponds with the measured coercivity very well, the value and the proportion of coercivity contributed from these three magnetic anisotropies vary with the epitaxial layer thickness.