Octylamine as a novel fuel for the preparation of magnetic iron oxide particles by an aqueous auto–ignition method

Magnetic particles were successfully synthesised by a new and simple one-step auto-ignition method, with octylamine as organic fuel and iron nitrate nonahydrate as an oxidant, both in an aqueous solution. After synthesis and stabilising at 550 °C in reduced atmosphere, the samples consisted of mostly well crystalline magnetite (Fe3O4), with a small amount of hematite present, in the form of micron–scale agglomerations of nanoparticles. A noticeable reduction of crystallite size of magnetite (42–28 nm) and an increase in the hematite crystallite sizes were observed with increasing octylamine addition, although the actual observed nanoparticle size increased slightly from ∼30 up to 50 nm. The magnetic properties were assessed at room temperature, and all were found to be strongly ferrimagnetic with very narrow hysteresis loops. The saturation magnetisation at 4 T was 77.2–91.6 A m2 kg−1, and coercivity was only 10.03–11.30 kA m−1 (126–142 Oe). These results are also compared to the few previous studies on using octylamine to produce magnetite nanoparticles, which were all purely organic hydrothermal processes, and produced materials with lower magnetisation values and comparable coercivity in similarly sized particles.