Abstract
This study focuses on cobalt and iron ordering within a ferrite structure CoxFe3-xO4, formed during a solid-state reaction of ?-Fe2O3 and CoCl2. A unique combination of transmission and emission Mössbauer spectroscopy was employed to inspect selectively the positions of iron and cobalt atoms in the structure. The comparison of transmission and emission spectra allowed the determination of tetrahedral and octahedral positions occupation. The presented method of combining the two Mössbauer spectroscopy techniques is suitable for any compounds containing both iron and cobalt atoms. Additional information concerning the samples composition and morphology were obtained by X-ray powder diffraction and scanning electron microscopy. An increased level of Co atoms incorporation into the structure of ferrite was revealed when higher amounts of Co entered the reaction.
Highlights
Cobalt ferrites are thoroughly investigated because of their magnetic, optical and electrical properties and their wide range of technological applications such as transformer cores, batteries, recording heads, ferrofluids, biomedical applications including biosensors and cellular therapy, catalysis and sensors.[1,2,3,4,5,6,7,8,9,10] Cobalt ferrite is a magnetically hard material with a high positive magnetic anisotropy constant, good chemical stability, high mechanical hardness and high level of magnetization
The specific properties of cobalt ferrites are governed by their microstructural arrangement that is formed during their synthesis
The samples of cobalt ferrites containing various amount of consisted of AX (Co) atoms were prepared by a solid-state reaction of hematite and cobalt chloride
Summary
Cobalt ferrites are thoroughly investigated because of their magnetic, optical and electrical properties and their wide range of technological applications such as transformer cores, batteries, recording heads, ferrofluids, biomedical applications including biosensors and cellular therapy, catalysis and sensors.[1,2,3,4,5,6,7,8,9,10] Cobalt ferrite is a magnetically hard material with a high positive magnetic anisotropy constant, good chemical stability, high mechanical hardness and high level of magnetization. The basic cell of MeFe2O4 spinel ferrite, where Me refers to the metal atom, is a cubic close-packed structure containing 32 anions.[14] Cations occupy two different crystallographic sites, namely A and B positions. Cations localized at A positions are surrounded by 4 oxygen atoms forming a tetrahedron, this position is referred to as tetrahedral. In the normal structure all the non-iron cations are located in tetrahedral positions. The opposite extreme, the inverse structure, has all the non-iron cations in octahedral positions according to the formula (Fe)[MeFe]O4. Cobalt ferrites usually form the inverse structure, where Co2+ ions are located only in B positions and Fe3+ ions are situated in both A and B positions. The emission arrangement offers information selectively on the local structure around the 57Co atoms The combination of these two complementary information allows to determine the degree of inversion. The correlation of cobalt and iron Mössbauer spectra could bring new enlightenment to the problem of cobalt ferrite structure formation
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