Different grades of magnetic cobalt ferrite (CoxFe3−xO4) nanoparticles were synthesized with various molar ratios of Fe 2+ to Co 2+ ions in the initial salt solutions method with using contact non-equilibrium plasma. The crystal structure and morphology of the nanoparticles are obtained from X-ray diffraction and transmission electron microscopy studies. With an increase in the value of x, the saturation magnetization for the samples of CoFe2O4 has decreased from 150.9 emu/g to 1.2 emu/g. The dependence of the coercive force on x is extremal with a plateau maximum corresponding to the x = 0.5-1.25.
Представлені результати експериментальних досліджень процесу фазоутворення в системі Fe 2+ /Co 2+ /O 2 /H 2 O в широкому діапазоні рН. Показано вплив присутності іонів Co 2+ , величини рН вихідного розчину, температури і кількості окислювача на фазовий склад отриманих продуктів. Встановлено, що присутність іонів Co 2+ прискорює процес окислення сполук Fe 2+ Ключові слова: сульфат заліза, гідроксид заліза, оксигідроксид, магнетит, каталітичне фазоутворення, кобальт (II), кисень Представлены результаты экспериментальных исследований процесса фазообразования в системе Fe 2+ /Co 2+ /O 2 /H 2 O в широком диапазоне рН. Показано влияние присутствия ионов Co 2+ , величины рН исходного раствора, температуры и количества окислителя на фазовый состав полученных продуктов. Установлено, что присутствие ионов Co 2+ увеличивает скорость процесса окисления соединений Fe 2+ Ключевые слова: сульфат железа, гидроксид железа, оксигидроксид, магнетит, каталитическое фазообразование, кобальт (II), кислород
Phase diagrams and spontaneous magnetization are rigorously calculated for a coupled spin-electron model on a doubly decorated honeycomb lattice, which accounts for a quantum-mechanical hopping of the mobile electrons on decorating sites, the nearest-neighbor Ising coupling between mobile electrons and localized spins, as well as the further-neighbor Ising coupling between the localized spins placed on nodal sites. The spontaneously ordered ferromagnetic phase, spontaneously ordered antiferromagnetic phase and disordered paramagnetic phase emerge in a phase diagram depending on an electron filling of the decorating sites, a relative size of the hopping term and both considered coupling constants. It is evidenced that a nature and size of the further-neighbor Ising coupling between the localized spins basically influences rise and fall of reentrant transitions close to a phase boundary between the paramagnetic phase and both spontaneously ordered phases.
The purpose of this study is to determine the phase composition of iron oxide compounds formed during precipitation by ammonium carbonate hydrolysis products, to establish the magnetite formation regions and the kinetic characteristics of the reaction formation Fe3O4. Characterization by X-ray diffraction (XRD) indicated that magnetite is formed in a solution of ferrous sulphate during the hydrolysis of ammonium carbonate. It has a homogeneous phase composition and a cubic crystal structure. Phase diagrams of the formation of the crystalline phase of magnetite, goethite and ferric hydroxide have been determined. It has been established that magnetite with a spinel structure is formed under controlled slow precipitation from ferrous sulphate with an ammonium carbonate solution. The calculation of the kinetic characteristics of the reactions of solid phase precipitation (a rate constant at different initial concentrations of ferrous sulphate, the order of the reaction) has shown that the process proceeds in two stages with the formation of an intermediate compound and its further oxidation. Moreover, the rate constant of oxidation is 0.654 L/min mol, and the rate constant of the first reaction is much higher – 1.645 L/min mol.
Currently, when nanomaterials have opened a new era in materials science, the study of the influence of synthesis conditions on the phase composition requires more attention. Ferrite nanoparticles have demonstrated immense popularity in the field of biomedicine due to their widespread use for cell separation, contrast agents, means for magnetically induced hyperthermia, in particular in the treatment of tumors. Chemical methods are considered as basic in the technology of nanomaterials production. In this work, nano-dispersed cobalt ferrite was synthesized by a two-stage method of coprecipitation and subsequent treatment with contact low-temperature nonequilibrium plasma (CNP). Since solutions treated with plasma, containing radicals, peroxides, have oxidizing properties, such chemically "activated" solutions can be used to produce cobalt ferrites. Formed oxidizing agents, initiate the formation of oxides of iron and cobalt. Thus, it has been established that, under the influence of contact plasma, hydrogen peroxide in solutions rapidly reacts with the formation of cobalt ferrite. The influence of the processing of KNP on the structural and magnetic properties of cobalt ferrite has been investigated. X-ray diffraction analysis, infrared Fourier transform spectroscopy (IR), and vibrational magnetometry (at room temperature) were used to determine the structural and magnetic properties. Infrared spectroscopy in the range from 400 to 4000 cm-1 confirmed the internal cationic vibrations of the spinel structure. The IR spectra showed the presence of absorption at 3414, 1617, 592 and 420 cm-1. The last two bands can be attributed to cation oscillations in tetrahedral and octahedral positions in CoFe2O4 spinel. X-ray phase analysis showed the formation of cobalt ferrite as a single phase. X-ray diffraction analysis and TEM showed that the resulting cobalt ferrite was obtained in the nano range. The average particle size, measured using TEM microscopy, was 30-50 nm. The saturation magnetization 58-61 Am 2 / g corresponds to the estimate of other authors. The coercivity is about 450 Oe, which is higher than for dispersed materials obtained by other methods.
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