Enhancing NiZn ferrite properties through microwave sintering: A comparative study

The structural, microstructural, morphological, and electromagnetic properties of a micro- and nanostructured nickel–zinc ferrite ((Cu_0.12Ni_0.23Zn_0.65)Fe₂O₄) were studied after sintering between 900 and 1100 °C. The microparticulated ferrite (MICRO) was a commercial material, while the nanoparticulated ferrite (NANO) was obtained through high energy milling of the former. The effect of microwave heating (MW), compared to traditional infrared sintering (IR), was investigated.

Microwave sintering successfully controlled the grain growth of both granulometries and produced sintered bodies with high relative densities (low porosity), small average grain size, narrow grain size distribution, and a high value of the complex magnetic permeability-imaginary part (μ″) for the MICRO ferrite. In the case of the NANO ferrite, microwave sintering yielded values similar to those obtained by conventional IR.

Microwave sintering significantly affected the densification and grain growth processes for both granulometries studied. Additionally, reducing the granulometry of the starting ferrite powder had a noticeable impact on the microstructure and electromagnetic properties of the sintered ferrites, regardless of whether microwave or infrared radiation was used. However, the magnetic property (μ″) decreased when the particle size of the starting powder was reduced from micro to nanometric scale, irrespective of the sintering source. This observation is supported by our previously published mathematical models that establish relationships between the complex magnetic permeability, magnetization mechanisms, angular frequency, and ferrite microstructure.