Hidenobu Umeda

Influence of Al2O3 Addition on the Temperature Dependence of Initial Permeability of NiCuZn Ferrites

The effect of Al2O3 addition on the temperature dependence of the initial permeability and microstructure of NiCuZn ferrites is investigated. The temperature dependence of initial permeability decreases with an increase in Al2O3 addition. EPMA analysis reveals that Al2O3 dissolves in the NiCuZn ferrite grains but is not uniformly dispersed. Separation of the initial permeability into two components, one due to spin rotation and the other due to domain wall motion, reveals that with an increase in the Al2O3 addition, the temperature dependence of the domain wall motion component decreases, while that of the spin rotation component shows no notable change. This indicates that the decrease in the temperature dependence of initial permeability may be attributed to the influence of Al2O3 on the domain wall motion.

Relaxation Phenomena of MgCuZn Ferrites

The decrease of initial relative permeability at 103-106Hz is observed in MgCuZn or MnMgCuZn ferrites. By measuring the temperature dependence of loss factor, the gradual deterioration of initial relative permeability is attributed to a relaxation phenomenon. The relaxation phenomena of MnMgCuZn ferrites occur in the condition of the stoichiometoric composition and the higher sintering temperatures. The activation energies of the relaxation phenomena are calculated to be 0.3-1.0eV. The relaxation times at infinite temperature are calculated to be 10-12-10-16 second. The initial relative permeability of MgCuZn or MnMgCuZn ferrites with the relaxation phenomena is higher than the value calculated from the resonance frequency and Snoek’s limit law.