Abstract: MnO₂ was introduced to NiCuZn ferrite. The effects of Mn substitution on the magnetic properties and microstructure of the (Ni_0.2 Cu_0.2 Zn_0.6)_1.03 (Fe₂O₃)_0.97+0.97xMnO₂ ferrite (x=0.1～0.5) were investigated. Mn content increases the initial permeability, but excess Mn content will result in the formation of a secondary phase. And the initial permeability depending on temperatures is strongly affected by Mn content too. When x≥ 0.4, the temperature coefficient of initial permeability increases quickly, which just like the relaxant phenomenon in ferroelectrics.

Key words: NiZnCu ferrite, Mn doped, initial permeability, relaxant phenomenon