Synthesising dispersed powders of CoZn ferrites for microwave absorption

Abstract

An important task of chemical materials science is to obtain materials with set parameters and to provide a reliable prediction of their properties. At the moment, an important task is to develop promising absorbing coatings based on dispersed magnetic materials. To ensure more effective use of dispersed powders of cobalt-zinc ferrite for fillers absorbing microwave radiation, we studied the changes in their magnetic properties and morphology depending on the conditions of the sol-gel synthesis. In our study, we synthesised Co0.65Zn0.35Fe2O4 ferrite powders of various degree of dispersion using the sol-gel method. The samples were analysed using X-ray diffractometry. The microstructure and the morphology of the nanoparticles were studied by means of scanning electron microscopy. The ratio of the concentration of metal atoms in ferrite powders and the features of their distribution on the surface of the particles were determined by energy dispersive X-ray spectroscopy. Magnetometry was used to determine the specific saturation magnetization and the coercive force. The study demonstrated that the main factor resulting in low values of the saturation magnetization of the cobalt ferrite nanopaticles is the formation of the magnetic dead layer on their surface. This layer is formed due to a number of factors including noncollinearity of spins, disordering of cations, defectiveness, amorphous state, and the difference in the composition occurring because the processes of reciprocal diffusion of cations during and the formation of the spinel structure during the synthesis are not complete. The study determined the ways to reduce the size of the inactive magnetic layer by controlling the parameters of the solgel synthesis in order to find effective methods of obtaining ferrite powders with increased magnetization, degree of crystallinity and the intermediate particles size between a superparamagnetic and a multidomain state. Such materials can be used as fillers for coating absorbing microwave radiation.

Keywords

• cobalt-zinc ferrite
• microwave absorption
• sol-gel synthesis
• nanoparticles