MAGNETIC PROPERTIES OF HIGH Bs MnZn FERRITES

摘要

Magnetic properties of manganese zinc ferrites with high saturation magnetic flux density (Bs) were investigated. A Bs of more than 500 mT at 100℃ was obtained with the composition where Fe_2O_3 is approximately 64mol% or more. In Fe-rich compositions, an increased number of cation vacancies were generally observed. This causes changes in magnetic properties as time elapses. The cation vacancies also causes the deterioration of core loss (Pcv) and initial magnetic permeability. In addition, B-H hysterisis loop, known as a "perminvar-loop", is typically observed for such composition. By sintering under low oxygen partial pressure (P_(O2)), the number of cation vacancies were reduced and the normalization of B-H hysterisis loop was observed. However Pcv and Hc also increased. One cause of this is Zn vaporization. The depth of Zn vaporized layer can be evaluated as 180μm. Another cause is the decrease of electrical resistivity. The total electrical resistivity is dominated by that at grain boundary. We also studied the cooling rate, which controls the resistivity at grain boundary.