Microstructure of magnetic materials greatly influences the performance of magnetic properties, and sintering has been used as an agent to tailor the microstructure of these magnetic materials especially ferrites. Nanostructured ferrites prepared by high-energy milling method are often inherently unstable owing to their small constituent sizes, non-equilibrium cation distribution, disordered spin configuration, and high chemical activity. Therefore, sintering of the milled ferrites recrystallizes the nanostructure and causes its transition from an excited metastable (activated) state into the low-energy crystalline state. A better understanding of the response of nanoscale ferrites with changes in temperature is crucial not only for basic science (the development of an atomistic and microscopic theory of the mechanochemical processes) but also because of the technological high-temperature applications in catalysis, ferrofluids and information storage. This chapter discusses on two different sintering schemes, which are a commonly applied multi-sample sintering and a rarely adopted single-sample sintering. Experimental results of single-sample and multi-sample sintering of NiZn ferrites and yttrium iron garnet (YIG) were highlighted, and their microstructural consequences on the magnetic properties were also discussed.
Part of the book: Sintering of Functional Materials
Sintering is a common synthesis method for the fabrication of ceramics. The widespread use of sintering for the production of complex ceramic oxide especially ferrites has led to a variety of investigations on the subject. Top-down approach synthesis like mechanochemical process has recently been suggested as a promising synthesis method for replacing bottom-up approach synthesis methods like sintering, questioning its necessity for thermal treatment at high temperature. Understanding of sintering mechanism is crucial in order to optimize and enhance the advantages of sintering, which cannot be replaced by other techniques. In general, ferrites with particular set of behaviors require a particular set of microstructural properties influenced by the sintering steps. The main objective of this chapter is to understand how the increase of sintering temperature affects the microstructural evolution, in order to develop a fundamental science understanding for the mechanism of sintering. In the second part of this chapter, presentation of experimental results on sintering of mechanically activated Ni0.5Zn0.5Fe2O4 nanoparticles and its effect on microstructural, magnetic, and optical properties was reported. Lastly, a comparative study between sintering (bottom-up approach) and mechanochemical (top-down approach) process is presented.
Part of the book: Sintering Technology