Role of Microwave Sintering in the Preparation of Ferrites for High Frequency Applications

Abstract

It is proven that the microwave sintering method is the truly low temperature method for the preparation of nanocrystalline magnetic oxide materials of diff erent sizes and shapes. Th is method saves time, energy, and cost. Th e materials can be produced in either a batch or continuous process using the said method. Th e key novelty of our work is the use of microwave sintering to dramatically enhance the kinetics of crystallization by one to two orders of magnitude. Th is paper will summarize the results obtained on various systems of soft ferrites, and Garnets (Ni-Cu-Zn ferrites, Mg-Cu-Zn ferrites, Ni-Zn ferrites, Co-Zn ferrites, Mn-Zn ferrites, YIG and GdIG, etc.), which were prepared by using microwave sintering method for various applications such as multilayer chip inductors, high frequency, microwave devices, and multilayered transformer cores, etc. All of these systems were sintered at a low temperature of 900 o C/ 30 minutes. Th e phase identifi cation, crystallinity, and morphology of the prepared powder were characterized by X-ray diff raction and transmission electron microscopy (TEM). Th e ferrites obtained with grain sizes varying from 80 nm to120 nm with high surface area ~ 26.8 m 2 g -1 to 156 m 2 g -1 . Th e performance of the sintered ferrites has been estimated from the studies of dependence of complex permittivity and permeability spectra on the frequency and temperature and it was found that the microwave sintered ferrites show improved dielectric and magnetic properties over conventionally sintered ferrites.