Microstructures and magnetic properties of sintering Mn–Zn ferrites with additive of different nanosized SiO 2 particles

Initial permeability μ_i and power loss of Mn–Zn ferrites doped with CaO and nano SiO₂ with different mean sizes were investigated. With increasing particle size of nano SiO₂, the temperature stability of μ_i became higher. Meanwhile, the power loss decreased. Microstructure analysis showed that Zn_0.4Mn_0.6Fe₂O₄ spinel structure was completely formed in the sintering samples, and SiO₂ reacted with CaO to form CaSiO₃ at the grain boundary. The effect of different particle sizes of SiO₂ on magnetic properties mainly depended on their influence on the grain size and the volume fraction of grain boundary phase. In detail, smaller particle size had higher surface activity under the same sintering condition, which led to excessive grain growth that influenced the grain size and its uniform, and also the volume fraction of grain boundary phase.