FemOn–Fem–xTixOn composites, complex iron oxides doped with titanium, have been synthesized
by coprecipitation (Cp series) or precipitation on preliminarily obtained magnetic particles (P
series) followed by hydro- or solvothermal treatment. The results of magnetometry, scanning
electron microscopy, X-ray diffraction, X-ray fluorescence, X-ray photoelectron and M¨ossbauer
spectroscopy reveal the presence of three main fractions: chemically inhomogeneous strongly
magnetic particles (maghemite/magnetite-titanomagnetite), weakly magnetic particles (hematite,
goethite and possibly other iron hydroxides) and superparamagnetic particles belonging to
the first two fractions. Samples of the Cp series where magnetically stable particles dominate are
clearly distinct from the P series, which is dominated by superparamagnetic particles. Theoretical
estimations of the hysteresis characteristics based on the model of magnetostatically interacting
two-phase particles are in the best agreement with the experimental data at characteristic particle
sizes of 60 nm for the Cp series and 13 nm for the P series.