Chemistry, Physics and Technology of Surface

ISSN 2518-1238 (Online), ISSN 2079-1704 (Print)

A method of synthesis of the nanocrystals of solid solutions of lanthanum-yttrium ferric garnet (Y_1-xLa_x)₃Fe₅O₁₂ (x – molar fraction) by co-precipitation of yttrium, lanthanum and iron hydroxides in boiling water has been developed and tested. Microwave electromagnetic radiation was used to initiate chemical reactions in aqueous precursor solutions, to control the nucleation process and to form new phases. The power of ultra-high frequency (microwave) radiation varied from 0.14 to 1.4 kW, changing the effective pulse duration of the process. The radiation frequency was 2.45 GHz for the period 6÷66 min. The solution was cooled to room temperature, then an aqueous solution of ammonia was added dropwise with vigorous stirring in the amount necessary to precipitate completely Y³⁺, La³⁺ and Fe³⁺ cations. The pH value of the reaction was maintained at 8÷12. After addition of ammonia, the stirring was continued for another 15 min, then the precipitate was filtered, washed with decantation until the specific conductivity of the supernatant was reduced to less than 2 μS/cm. It has been found that the developed synthesis method provides the production of a powder of a given composition in the form of nanoparticles (NP) in a shape close to spherical. The mutual solubility of Y₃Fe₅O₁₂ and La₃Fe₅O₁₂ in the state of solid solutions, their crystal structure, morphology, and magnetic properties were investigated. The average diameter of the obtained NP, dependent on the concentration of precursors and the process time, ranged from 20 to 60 nm, the average specific surface area varied from 75 to 25 m²/g, respectively. X-ray analysis confirmed the formation of a phase of a solid solution of substitution with the structure of garnet at x < 0.75. The vibration magnetometry method obtained the hysteresis loops of dipole-dipole non-interacting NP solid solutions and the dependence of their saturation magnetization and coercive force on the lanthanum molar fraction. Due to their magnetic properties, these solid solution nanoparticles are promising for use in medicine as agents for hyperthermia, for targeted drug delivery in magnetic therapy, in magnetic resonance imaging, and for the diagnosis of diseases using the magnetic separation method.

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