This study is focused on a simple and fast synthesis of nonstoichiometric magnetite nanoparticles with the chemical formula Fe3−XO4 and magnesium ferrite nanoparticles (Mg1−XFe2+XO4). The nanoparticles were prepared with Fe2+ ions (FeSO4 · H2O) alkalised by KOH under oxidative conditions and in a microwave field. X-ray powder diffraction (XRD) and 57Fe transmission Mössbauer spectroscopy were used to determine the phase composition and crystal structure in detail. The presence of synthetic magnetite, maghemite, goethite, and magnesium ferrite was observed. Room temperature Mössbauer spectroscopy revealed the existence of ferromagnetic sublattices and superparamagnetic fraction. The superparamagnetic component corresponds to magnesium ferrite nanoparticles. Low temperature Mössbauer spectroscopy was used to locate the blocking temperature of superparamagnetic nanoparticles and to separate the sublattices. The presumed spherical morphology of nanoparticles and their size under 100 nm have been confirmed by transmission electron microscopy (TEM). The obtained results were used to provide possible reaction scheme, which serves to tailor the synthesis to a desired application.

Covering layers might have very important role in improving performance of many mechanical parts. These layers are usually designed to protect a substrate from the environment and enhance mechanical properties such as hardness. Blackening is a classical approach that is very demanding on resources. This process is based on the alkalisation of surface atoms and the transformation of formed hydroxides to oxides. Such an approach inspired us to carry out experiments resulting in preparation of protective layers with similar properties, by using stoichiometric spinel ferrite nanoparticles (MeFe2O4). Thus mechanical parts were covered with ferrite nanoparticles and heated in a furnace. Ferrite samples, which were used as precursor for the preparation of layers, were analysed with X-ray powder diffraction, energy dispersive X-ray spectroscopy and 57 Fe Mössbauer spectroscopy. The samples were analysed with ultrasonic hardness test, electron microscopy, and Mössbauer spectroscopy. The protection layers showed a higher hardness compared to untreated parts.

Two series of ZnFe2O4 mixed cubic spinel nanoparticles were prepared by a coprecipitation method, where a solution of Fe3+ and Zn2+ was alkalised by a solution of NaOH. While the first series was prepared by a careful mixing of the two solutions, the microwave radiation was used to enhance the reaction in the other series of samples. The effect of the microwave heating on the properties of the prepared particles is investigated. X-ray powder diffraction (XRD), 57Fe Mössbauer spectroscopy and magnetometry were employed to prove the cubic structure and superparamagnetic behavior of the samples. The particle size in the range of nanometers was investigated by a transmission electron microscopy (TEM), and the N2 adsorption measurements were used to determine the BET area of the samples. The stoichiometry and the chemical purity were proven by energy dispersive spectroscopy (EDS). Additionally, the inversion factor was determined using the low temperature Mössbauer spectra in the external magnetic field. The microwave heating had a significant effect on the mean coherent length. On the other hand, it had a lesser influence on the size and BET surface area of the prepared nanoparticles.