Microstructures and magnetic properties of low temparature sintering NiCuZn ferrite ceramics for microwave applications

Polycrystalline (Ni0.2Cu0.2Zn0.6O)(1.03)(Fe2O3)(0.97) (NiCuZn) ferrite ceramics with low ferromagnetic resonance (FMR) line width (Delta H) and high saturation magnetization (4 pi M-s) were synthesized at low sintering temperatures by adding Bi2O3-ZnO-Bi2O3 (BZB) glass additives. Furthermore, phase compositions, microstructures, and magnetic properties of the low-temperature-sintered NiCuZn ferrite ceramics were systematically analyzed. First, X-ray diffraction patterns showed that BZB glass has no obvious effect on phase structure of NiCuZn ferrites. Moreover, scanning electron microscopy images revealed that BZB glass can dramatically enhance grain growth and densification of the ferrites. More importantly, due to grain growth and reduction of porosity, Delta H of the NiCuZn ferrite sintered at 870 degrees C decreased significantly from 521.2 Oe to 150.5 Oe. Moreover, compact and uniform NiCuZn ferrites possessed high saturation magnetization (4 pi Ms =similar to 4267 Gauss), reduced coercivity (H-c = similar to 92.2 A/m), and large saturation flux density (B-s = similar to 269.1 mT). The above mentioned results indicated that low-melting point BZB glass is an optional sintering aid to promote grain growth and enhance gyromagnetic properties of NiCuZn ferrites sintered at low temperature.