Synthesis of Iron-Oxide nanoparticles: Size and shape effect on magnetic properties

Full text: Iron-Oxide nanoparticles with sizes between 5-18nm obtained by means of thermal decomposition and their static magnetic properties are reported. Sizes and shapes were tuned making small changes in the synthesis process (concentration of some of its reactive were varied). Furthermore, in one case, the final step of the synthesis was modified allowing the reaction to have contact with room atmosphere obtaining an increment on the average size of the nanoparticles and different geometries. Structural characterization, X-ray diffraction and TEM images was performed in different samples and related with magnetic measurements. Zero Field Cooled and Field Cooled (ZFC/FC) magnetization at several applied fields as well as hysteresis loops at different temperatures were measured. From these data it was possible to infer blocking temperatures, coercive field, saturation magnetization and log-normal size distribution of the nanoparticles (based on conventional superparamagnetism modelling). Values of anisotropies from ~2.8 x 10⁴J/m³ to ~7.9 x 10⁴J/m³) and saturation magnetization at room temperature (from ~37A.m²/kg to ~78A.m²/kg), were obtained, indicating a strong dependence on interactions, size and shape of the nanoparticles. (author)