Synthesis of nano-dimensional cobalt-zinc ferrites by the low-temperature spray-drying with subsequent thermolysis

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Co0,65Zn0,35Fe2O4nanoparticles were produced by spray-drying in air in presence of NaCl from the solution of nitrates, as well as from the suspension of coprecipitated particles. The precursors obtained were annealed at 300–900 °C in the matrix of the inert component in order to increase the crystallinity degree without substantial increase of the nanoparticle size. Microstructure, morphology and magnetic properties of nanoparticles were studied by XRD, FT-IR spectroscopy, TEM / SEM and magnetometry. For the ferrites obtained from nitrate solutions partial oxidation of Co2+ions to Co3+occurs, which leads to the formation of two spinel phases, ferrite and cobaltite. With the increase of annealing temperature the content of cobaltite decreases and content of ferrite increases. No cobaltite formation was observed for annealing the spray-dried suspension. An increase in the temperature of the heat treatment leads to partial recrystallization of the particles and the ordering of the ferrite crystal structure, which causes an increase in the specific magnetization of the materials: from 32.8 emu/g (before annealing) to 91.3 emu/g (annealing at 900 ° C). The average diameter of nanoparticles after heat treatment does not exceed 100 nm.