From Low to High Saturation Magnetization in Magnetite Nanoparticles: The Crucial Role of the Molar Ratios Between the Chemicals

Abstract

In this study, a comprehensive characterization of iron oxide nanoparticlessynthesized by using a simple one-pot thermal decomposition route is presented. In orderto obtain monodisperse magnetite nanoparticles with high saturation magnetization, closeto the bulk material, the molar ratios between the starting materials (solvents, reducingagents, and surfactants) were varied. Two out of nine conditions investigated in this studyresulted in monodisperse iron oxide nanoparticles with high saturation magnetization (90and 93% of bulk magnetite). The X-ray diffraction analyses along with the inspection ofthe lattice structure through transmission electron micrographs revealed that the maincause of the reduced magnetization in the other seven samples is likely due to the presenceof distortion and microstrain in the particles. Although the thermogravimetric analysis,Raman and Fourier transform infrared spectroscopies confirmed the presence ofcovalently bonded oleic acid on the surface of all the samples, the particles with higherpolydispersity and the lowest surface coating molecules showed the lowest saturationmagnetization. Based on the observed results, it could be speculated that the changes in the kinetics of the reactions, induced byvarying the molar ratio of the starting chemicals, can lead to the production of the particles with higher polydispersity and/or latticedeformation in their crystal structures. Finally, it was concluded that the experimental conditions for obtaining high-quality ironoxide nanoparticles, particularly the molar ratios and the heating profile, should not be chosen independently; for any specific molarratio, there may exist a specific heating profile or vice versa. Because this synthetic consideration has rarely been reported in theliterature, our results can give insights into the design of iron oxide nanoparticles with high saturation magnetization for different applications