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Metal-ferrite/maghemite nanocomposites (NiFe₂O₄/***$\gamma$-Fe₂O₃ and CoFe₂O₄/$\gamma$-Fe₂O${}_3)$ were synthesized via doping maghemite with metal salt (NiCl₂ or CoCl${}_2)$ followed by reduction of metal ions using NaBH₄. The synthesized metal-ferrite/maghemite nanocomposites were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), Fourier transform infrared (FTIR) and the amounts of the dopant-metal (Ni/Co) were determined using ICP-OES technique. Results showed that this synthetic route produced nanocomposites with highly active ferrite phases MFe₂O₄. The synthesized nanocomposites exhibited exceptional catalytic activities for the reduction of 4-nitrophenol and 2-nitroaniline as well as the catalytic degradation of methyl orange. Specific activity parameter of NiFe₂O₄/$\gamma$-Fe₂O₃ and CoFe₂O₄/$\gamma$-Fe₂O₃ toward reduction of 4-NP reached 993.9 and 929.8s${}^{-1}$g${}_{\mathrm{\text{metal}}}^{-1}$, respectively. These high values of specific activities are higher than most reported metal-ferrite composites prepared via traditional co-precipitation methods. Besides, strong magnetic properties of the prepared metal-ferrite/maghemites facilitates easy separation process for several reuses.

A comparative study of magnetic properties using the method of magnetometry with vibration magnetometer and spectra of electron paramagnetic resonance (EPR) nanocomplexes (NCs) of nanoparticles Fe₂O₃, Fe₃O₄ and antitumor antibiotic doxorubicin (DOXO) have shown that changes in saturation magnetic moments are similar to changes in integral intensity of EPR spectra. The greatest magnetic moments of saturation and integral intensity of EPR spectra were demonstrated by samples of Fe₃O₄ in NC with doxorubicin, which had the highest antitumor effect in radiofrequency hyperthermia of Walker-256 carcinosarcoma. The presented research provides the evidence of stronger antitumor effect of Fe₃O₄ and DOXO NC in comparison to NC from γ-Fe₂O₃ and DOXO at combined action of constant magnetic field and electromagnetic field. This can be a basis for development of bioengineering technology of magnetic cancer nanotherapy in conditions of moderate hyperthermia (< 39°C).