Manganese-zinc ferrites with improved properties

Mn-Zn ferrites play an important role for the design of inductors in the frequency range from 10 kHz to 100 MHz. Important intrinsic properties such as crystalline anisotropy, magnetostriction, and their dependence on chemical composition are well known. All properties can be improved regarding the present state of the art. The experiments are related to the optimization of microstructure, esp. the control of grain growth in the range of 1 to 50 mu m with a narrow distribution of the grain size, the insulation of the grain boundary and the control of defects. SEM and TEM was used to investigate the microstructure, amorphous interfaces and triple points of different additive systems. The following properties have been strongly influenced: Increase of initial permeability from 10.000 up to 20.000. Improvement of insertion loss for frequencies of up to 5 MHz for EMC applications. Decrease of power loss in the frequency range from 0.5 to 1 MHz for power applications. Therefore the use of optimized technology was necessary in order to obtain better homogenity of raw material and good densification of green bodies and optimum sintering. The sol-gel route gives a better chemical homogeneity, especially for sintering additives. The gained experiences hold out the prospect of improving the above mentioned properties furthermore.