CORE LOSSES AND MAGNETIC-PROPERTIES OF MN-ZN FERRITES WITH FINE-GRAIN SIZES

Mn-Zn ferrite with fine grains was obtained by sintering hydrothermal-precipitated ferrite powders. The average grain sizes of the hot isostatically pressed specimens were 1.0-6.8 mum and the relative densities were above 99.3%. The frequency at which the maximum value of mu'' was obtained for the ferrites tends to increase with decreasing grain size, and the core loss at 5 mT and 1-2 MHz attained a minimum value for the ferrite with grain size of 2-3 mum. At 80-degrees-C, which is practically the usual operating temperature, the core loss of this specimen is also considerably smaller than those of the commercial ferrites with grain sizes of 7.7-10.9 mum at 0.5-1 MHz. Therefore, the fine-grain ferrite is expected to be useful as a material for high-frequency transformers.