Mössbauer, magnetization and X-ray diffraction characterization methods for iron oxide nanoparticles

•KV parameter, obtained from Mössbauer spectra can be used for nanoparticle size characterization.•Mössbauer spectra of 10–25 nm nanoparticles can be effectively described by ferromagnetic model.•Surface impurities can cause incorrect nanoparticle size determination.

Water soluble magnetite iron oxide nanoparticles with oleic polymer coating and average diameters in the range of 5–25 nm, previously determined by TEM, were characterized using Mössbauer, magnetization and X-ray diffraction measurements. Comparative analysis of the results demonstrated a large diversity of magnetic relaxation regimes. Analysis showed the presence of an additional impurity component in the 25 nm nanoparticles, with principally different magnetic nature at the magnetite core. In some cases, X-ray diffraction measurements were unable to estimate the size of the magnetic core and Mössbauer data were necessary for the correct interpretation of the experimental results.