Effects of Bi2O3–MnO2 additives on tunable microstructure and magnetic properties of low temperature co-fired NiCuZn ferrite ceramics

The development of miniaturized high frequency ferrite ceramics is attracting widely interest for next generation MLCI (multi-layer chip inductors). However, there exist short comings in the microstructure adversely affecting magnetic properties. In this study, 0.5 wt% MnO 2 - x wt% Bi 2 O 3 ( x  = 0.1, 0.5, 1.0, 1.5, 2.0, and 3.0) were introduced into NiCuZn ferrites to adjust the microstructure at low temperatures. Also, the microstructure changes and high frequency magnetic properties of NiCuZn ferrites were investigated via controlling the addition of MnO 2 –Bi 2 O 3 and sintering temperatures. SEM results indicated that quantitative MnO 2 can suppress abnormal grain growth when optimized amount of Bi 2 O 3 was added. In addition, various amounts of Bi 2 O 3 were added to adjust the magnetic properties by controlling grain growth. Results revealed that 0.5 wt% MnO 2 -1.5 wt% Bi 2 O 3 composite addition is a critical point to enhance the homogeneity of the samples. Also, interestingly, the dominant contribution to dynamic magnetization mechanism changes from spin rotation to domain wall motion when the content of Bi 2 O 3 is greater than 1.0 wt%. Finally, fine microstructure of NiCuZn ferrites with high permeability ( μ ′ ≈ 291), high saturation magnetization ( M s ≈ 58.83 emu/g), high saturation flux density ( B s ≈ 290.04), high Q factor (~ 75) and enhanced cutoff frequency (~ 60 MHz) can be obtained sintered at 925 °C. Thus, this work may provide new guidance for developing RF frequency LTCC NiCuZn ferrite ceramics.