Ferrimagnetic nanoparticles are used in biotechnology (as drug carriers, biosensors, elements of diagnostic sets, contrast agents for magnetic resonance imaging), catalysis, electronics, and for the production of magnetic fluids and magnetorheological suspensions, etc. The use of magnetic nanoparticles requires enhanced magnetic characteristics, in particular, high saturation magnetisation.The aim of our study was to obtain single-phased magnetic nanoparticles of MnxFe3–xO4 solid solutions at room temperature. We also studied the dependence of the changes in their structure, morphology, and magnetic properties on the degree of substitution in order to determine the range of the compounds with the highest magnetisation value.A number of powders of Mn-substituted magnetite MnxFe3–xO4 (x = 0 – 1.8) were synthesized by means of co-precipitation from aqueous solutions of salts. The structural and micro-structural features and magnetic properties of the powders were studied using magnetic analysis, X-ray diffraction, transmission electron microscopy, and IR spectroscopy.The X-ray phase analysis and IR spectroscopy confirm the formation of single-phase compounds with cubic spinel structures. The maximum increase in saturation magnetization as compared to non-substituted magnetite was observed for Mn0.3Fe2.7O4 (Ms = 68 A·m2·kg–1 at 300 K and Ms = 85 A·m2·kg–1 at 5 K). This is associated with the changes in the cation distribution between the tetrahedral and octahedral cites.A method to control the magnetic properties of magnetite by the partial replacement of iron ions in the magnetite structure with manganese has been proposed in the paper. The study demonstrated that it is possible to change the magnetisation and coercivity of powders by changing the degree of substitution. The maximum magnetisation corresponds to the powder Mn0.3Fe2.7O4. The nanoparticles obtained by the proposed method have a comparatively high specific magnetisation and a uniform size distribution. Therefore the developed materials can be used for the production of magnetorheological fluidsand creation of magnetically controlled capsules for targeted drug delivery and disease diagnostics in biology and medicine (magnetic resonance imaging).
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