Alkali concentration effects on the composition, morphology and magnetic properties of magnetite, maghemite and iron oxyhydroxide nanoparticles

Iron oxide nanoparticles were obtained by co-precipitation from mixed iron salts and ammonium hydroxide (NH4OH) solutions. In this paper, solutions with different concentrations of ammonium hydroxide were used and its effect on composition and morphology were analyzed. Detailed morphological studies from transmission electron microscopy images reveal the presence of two different shapes: spheroidal and elongated nanoparticles. The samples produced with low concentrations of NH4OH showed elongated shapes in the order of 100 nm and 10 nm (length & width), and the samples produced with high concentrations of NH4OH exhibit a homogeneous size distribution of spheroidal particles of the order of 10 nm diameter. The structural analysis from x-ray diffraction elucidates the presence of different phases for samples produced with different alkali concentrations. From vibrating sample magnetometer measurements and MoEurossbauer spectroscopy on samples produced with high and low alkali concentrations, superparamagnetic and paramagnetic behavior was respectively observed. The magnetic nanoparticles production procedure presented here will not only be used in cutting-edge research but will also serve as a teaching tool to introduce undergraduate, master's and Ph.D. students.