The presented experimental research focuses on obtaining iron oxide nanoparticles with high efficiency for magnetic hyperthermia treatments. They were prepared by two different synthesis methods. The first sample was prepared in the modified process of thermal decomposition of Fe precursor in a polyol solution. The second sample was prepared by coprecipitation based on mixing iron salts solution with NaOH solution. Samples were characterized by X-ray powder diffraction, SQUID measurements, transmission electron microscopy and Zetasizer Nano series. The results derived from two systems obtained by different synthesis methods represent valuable knowledge in the fundamental research on magnetic behavior of nanoparticle systems and also a significant contribution in the developing field of application of magnetic hyperthermia.

Ni-doped goethite (α-FeOOH) nanorods were synthesized from mixed Fe(III)-Ni(II) nitrate solutions with various Ni/(Ni+Fe) ratios (0, 5, 10, 20, 33 and 50 mol % Ni) by hydrothermal precipitation in a highly alkaline medium using the strong organic alkali, tetramethyl¬ammonium hydroxide (TMAH). Ni-doped hematite (α-Fe2O3) nanorods were obtained by calcination of Ni- doped goethite nanorods at 400 °C. The Ni2+- for-Fe3+ substitution in goethite and hematite was confirmed by determination of the unit cell expansion (due to the difference in the ionic radii of Fe3+ and Ni2+) using XRPD and determination of the reduction of a hyperfine magnetic field (due to the difference in magnetic moments of Fe3+ and Ni2+) using Mossbauer spectroscopy. Single- phase goethite nanorods were found in samples containing 0 or 5 mol % Ni. A higher Ni content in the precipitation system (10 mol % or more) resulted in a higher Ni2+-for-Fe3+ substitution in goethite, and larger Ni-doped goethite nanorods, though with the presence of low crystalline Ni-containing ferrihydrite and Ni ferrite (NiFe2O4) as additional phases. Significant changes in FT-IR and UV-Vis-NIR spectra of prepared samples were observed with increasing Ni content. Electrochemical measurements of samples showed a strong increase in oxygen evolution reaction (OER) electrocatalytic activity with increasing Ni content.

Herein we present the results of specific loss power (SLP) analysis of polydisperse water based ferrofluids, Fe3O4/PEG200 and Fe3O4/PEG6000, with average Fe3O4 particle size of 9 nm and 11 nm, respectively. Specific loss power was measured in alternating magnetic field of various amplitudes and at fixed frequency of 580.5 kHz. Maximum SLP values acquired were 195 W/g for Fe3O4/PEG200 and 60 W/g for Fe3O4/PEG6000 samples. The samples were labeled as superparamagnetic by magnetization measurements, but SLP field dependence showed deviation from the behavior predicted by the commonly employed linear response theory. The scope of this theory for both samples with wide particle size distribution is discussed. Deviation from the expected behavior is explained by referring to polydisperse nature of the samples and field dependent relaxation rates.