This paper investigates a method to achieve a close to superparamagnetic behavior in Ni-Al2O3 nanocomposite synthesized by solution combustion. The starting materials used are nickel and aluminum nitrates, as oxidizers, and urea, as fuel. Samples with 3, 10, 15, 25, 35 and 45 wt.% alumina are produced on a hot plate at 330 °C in air. The results show that the change in the content of Al2O3 can change the size of nickel crystallites and particles. The nickel particle size decreased by increasing the alumina content (from about 644 nm to 38 nm) and resulted in linear hysteresis loops and a relatively high magnetic saturation. The smallest mean nickel particle size measured using TEM images was larger than the critical size that indicates a typical superparamagnetic behavior. The observed linear hysteresis loops and the close to superparamagnetic behavior observed in the nanocomposite are mainly attributed to the combination of two different magnetic behaviors of ferromagnetic nickel and diamagnetic alumina.

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