Synthesis of a low loss Mn-Zn ferrite for power applications

Current market trends of the switching power supplies industry require even lower energy losses in power conversion systems with maintenance of satisfactory initial permeability levels. Typical operation conditions refer to a frequency of 100 kHz, an induction level of 200 mT and a steady state temperature of 100° C. In this work the development of a polycrystalline Mn-Zn ferrite material that exhibits initial relative magnetic permeability above 2500 and very low power losses at 100 kHz, 200 mmT and 100° C is presented. The Mn-Zn ferrite samples were prepared by the conventional solid state reaction method. Sintering was performed under controlled atmosphere conditions. The combinatorial role of TiO2 and CoO together with Zn content, as well as the effects of the process parameters on the magnetic performance of the Mn-Zn ferrite was evaluated. It is shown that the development of the adequate polycrystalline microstructure that is characterized by (a) high sintered density, (b) homogenous grain size that is free of morphological or chemical pinning defects and (c) high resistivity grain boundary structure, can be achieved by means of appropriate compositional and dopant adjustment, anisotropy control and specific resistivity optimization. The newly developed Mn-Zn ferrite is characterized by high sintered density of 4.91 g/cm3, initial magnetic permeability of 2512 (at 10 kHz, 0.1 mT, 25 °C), high saturation magnetic flux density of 560 mT (at 10 kHz, 1200 A/m, 25 °C) and very low power losses (Pv) of 224 mW/cm3 (at 100 kHz, 200 mT, 100 °C) combined with very low power losses of 470 mW/cm3 even at room temperature, establishing it as ideal for power applications.