A New Low Loss MnZn Ferrite Designed to Use in the High Temperature Range above 100°C

Abstract

A new MnZn ferrite with low core loss, P_cv and high saturation flux density, B_s above 100°C have been developed as a material suitable for transformer or inductor cores, which operate in the high temperature range from 130 to 150°C. The material with the B_s of 400 mT at 140 ºC and the P_cv of 286 kW/m³ at 140°C, 100 kHz and 200 mT have been obtained, and it is most suitable for onboard power supplies etc. The magnetic properties of the core were realized by choosing the desired compositions and optimizing the sintering conditions. In order to decrease the P_cv and to increase the B_s, it is necessary to select a composition in which magnetic anisotropy and magnetostriction are zero in the ternary system of MnO-ZnO-Fe₂O₃ and to add NiO to the main composition. Furthermore, by controlling the temperature and the atmosphere precisely in sintering, the adequate uniform grains and the grain boundaries, in which trace additives are precipitated, are realized in the core which is as free as possible from defects, pores, impurities, etc. within grains at the same time, and thereby the low loss and the high saturation flux density were improved in the high temperature range above 100°C.