Low-temperature sintering of Ni-Zn-Cu ferrite and its permeability spectra

The low-temperature sintering of Ni-Zn-Cu ferrite was investigated using the usual ceramic technique. We found that the post-sintering density and the permeability of the sintered ferrite are strongly affected by the size of the starting oxide powders and the pre-sintering temperature. The most effective method of preparing high-permeability ferrite is to utilize fine particles of iron oxide and to calcine at about 800 degrees C. Sintered ferrite with a density greater than 4.5 g/cc and a permeability at 10 MHz greater than 200 can be obtained at a relatively low sintering temperature (about 900 degrees C). This condition is suitable for producing multilayer chip inductors. Additionally, the complex permeability of sintered ferrite was well-described as the summation of the spin rotational contribution and the domain wall motion component. The permeability in the 100 MHz region was determined mainly by the spin rotation magnetizing mechanism and then it depended only on the ferrite volume loading, i.e. the post-sintering density. However, the contribution of the domain wall motion was not negligible in the 10 MHz region and the domain wall contribution was controlled both by altering the post-sintering density and by varying the ferrite grain size.