MAGNETIC-PROPERTIES AND THE GRAIN-BOUNDARY STRUCTURE OF MN-ZN FERRITES WITH THE ADDITION OF NB2O5

The effects of the addition of Nb2O5 on the power losses in manganese-zinc ferrites have been investigated by measuring the magnetic properties and observing the grain boundary structures. The addition of Nb decreases the initial permeability and raises the resonance frequency. Power losses were analyzed as the sum of the contributions of hysteresis loss, eddy current loss and residual loss. The hysteresis and eddy current losses were reduced by about 10% by the addition of Nb below 200 kHz, in spite of the smaller magnetic permeability. These losses are thought to originate from the additive effect of Nb atoms, which are enriched in grain boundaries to form a high-resistivity layer and prevent Ca and Si atoms being incorporated with the spinel lattice. The residual losses were greatly reduced by the addition of Nb at higher frequencies. The origin of the difference in the residual losses is discussed.