Influence of fuel-to-oxidizer ratio on the magnetic properties of Fe-doped In2O3 nanoparticles synthesized by solution combustion method

Two series of (In_1−xFe_x)₂O₃ were prepared by a solution combustion method using different fuel-to-oxidizer (i.e. glycine/metal nitrate, G/N) ratios. The crystal structure and magnetic properties of the compounds were investigated by means of X-ray diffraction, transmission electron microscopy and magnetic measurements. Detailed structural analysis shows the solubility limits of Fe in In₂O₃ are x=0.08 and 0.45 for the G/N ratios of 5/4 and 5/6, respectively. Crystallite size of the samples prepared with the G/N ratio of 5/6 is much smaller than that of the samples prepared with the G/N ratio of 5/4. At room temperature, the sample with x=0.01 prepared with the G/N ratio of 5/4 is paramagnetic and those with x=0.03-0.07 are ferromagnetic, whereas the samples with x=0.15-0.45 prepared with the G/N ratio of 5/6 show superparamagnetic behavior and those samples with x<0.15 are paramagnetic. Different magnetic behavior of these two series of samples could be attributed to different origins of magnetism. The magnetism of the samples prepared with the G/N ratio of 5/4 might originate from the existence of mixed valence Fe ions whereas the magnetism of the samples prepared with the G/N ratio of 5/6 could be due to the small crystallite size.