The dissertation is dedicated to solving a number of important tasks in the physics of magnetism - to find out the patterns of changes in the static and dynamic magnetic characteristics of ferrite-spinel nanoparticles and composites based on them, depending on their chemical composition. With the help of a wide arsenal of experimental methods, including vibrational magnetometry,
calorimetric measurements, electron microscopy, X-ray structural analysis, a detailed study of real ensembles of magnetic nanoparticle ferrite-spinels (Ni,Zn)Fe2O4 and composites CoFe2O4/Fe3O4 and Fe3O4/CoFe2O4 with a core/shell structure, magnetic nanoparticles NaFeO2, which in the bulk state are non-collinear antiferromagnet. Based on the analysis of the obtained experimental
data and the conducted numerical simulations, important conclusions were made that indicate possible methods of developing nanomaterials with optimized and controlled magnetic characteristics, promising for various technical and medical
applications, such as heat inducers for magnetic hyperthermia.
The first chapter of the thesis discusses the general properties of magnetic nanoparticles in the context of biomedical applications. The necessary requirements for the creation of nanomaterials with controlled and reproducible structural, magnetic, and thermal characteristics and exposure methods for obtaining parameters corresponding to the tasks are substantiated.
Special attention is paid to nanomaterials for use in magnetic hyperthermia. Based on the review of the works, conclusions are made about the requirements for the size of such nanoparticles and their respective dispersion, about the need for ferro(ferro)magnetic nanoparticles to be in a single-domain state, and about the issue of biocompatibility of magnetic nanoparticles.
As a result, conclusions were drawn about the current state of research on the properties of magnetic nanoparticles for biomedical applications, and the purpose of the work and scientific tasks, which were aimed at solving the research presented in this work, were formulated.
The second chapter provides a detailed description of the fabrication conditions and research methods of the nanoparticles ensembles and nanocomposites, which were studied in accordance with the assigned tasks.
The third chapter presents the results of systematic studies of magnetic and calorimetric properties of the ensembles of Ni1-xZnxFe2O4 nickel-zinc ferrite nanoparticles over a wide range of concentrations 0 ≤x≤ 0.8. It has been experimentally confirmed that under the application of an alternating magnetic field, the heating efficiency of magnetic nanoparticles significantly decreases
when their temperature approaches the Curie point, which allows the development of the systems that prevent overheating of the target heating area. The range of concentrations within which the parameters of magnetic nanoparticles meet the requirements necessary for their use in self-controlled magnetic hyperthermia has been determined.
In the fourth chapter, a procedure for in-depth analysis of the magnetic parameters of nanoparticles is proposed, as well as the results of studies of composite nanoparticles with a core/shell architecture, which consist of magnetically hard and magnetically soft materials, are presented. The purpose of the work, the results of which are presented in this section, was to understand the influence of the core/shell architecture on the magnetization and effective anisotropy of composite nanoparticles CoFe2O4/Fe3O4 and Fe3O4/CoFe2O4; calculation, measurement and analysis of specific power losses under the action of an alternating magnetic field, as well as to find a method of the fabrication of magnetic nanoparticles with controlled magnetic parameters for various
technological and biomedical applications.
The fifth chapter presents the results of magnetic and calorimetric studies of an ensemble of NaFeO2 nanoparticles. It is noted that NaFeO2 bulk samples are non-collinear antiferromagnets with negligibly small resulting magnetization.
However, when moving to nanoscale dimensions, these materials demonstrate a relatively high magnetization, which is comparable to the magnetization of ferritespinels. The mechanisms of energy losses under the conditions of action of a variable magnetic field have been clarified. It is shown that magnetic nanoparticles of NaFeO2 are promising for the use in medicine, in particular as contrast agents in magnetic resonance imaging or heat inductors in magnetic
hyperthermia.
