Microwave sintering of nanocrystalline Ni _1-x Zn _x Fe ₂ O ₄ ferrite powder and their magnetic properties

Nanocrystalline Ni_1-xZn_xFe₂O₄ (0 ≤ x ≤ 1.0) powder with grain size of 30 nm was prepared using the spraying-coprecipitation method. The obtained nanocrystalline Ni _1-xZn_xFe₂O₄ powder was sintered using conventional and microwave sintering techniques. The results show that the microstructure and magnetic properties of the sintered samples are obviously improved by microwave sintering of nanocrystalline Ni_1-xZn _xFe₂O₄ ferrite powder. The initial permeability of Ni_1-xZn_xFe₂O₄ ferrite increases with the increase in zinc concentration, although its resonance frequencies shift from high frequency to low frequency. The maximum initial permeability for microwave-sintered Ni_0.4Zn_0.6Fe₂O₄ ceramic obtained at the temperature of 1170°C for 30 min reaches up to 360.9, and its resonance frequency is ~10 MHz. It may be attributed to the nanocrystalline Ni_1-xZn_xFe₂O₄ raw powder as well as the microwave sintering process, which results in a synergistic effect on improvement of the microstructure and magnetic properties.