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 Mossbauer, 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 Mossbauer data were necessary for the correct interpretation of the experimental results.
