Sonochemically assisted synthesis of zinc-doped maghemite.

Nanoparticles of zinc-doped maghemite were prepared using ultrasonic radiation. As a precursor, a suspension of maghemite in an alkaline aqueous solution of zinc nitrate at pH 9 was sonicated. The zinc-doped maghemite nanoparticles were investigated by X-ray diffraction, Mössbauer spectroscopy, high-resolution electron microscopy (HREM) and SQUID magnetometry. The Mössbauer measurements, which cover the temperature range 4.2 K to room temperature, were acquired in zero field and an applied field of 5 T. The results show that by using ultrasound radiation, zinc Zn2+ can substitute for Fe3+ up to a composition close to zinc ferrite (ZnFe2O4), which has a random distribution of Fe3+ ions over both A and B sublattices in the spinel structure with an inversity parameter of delta=0.322. This leads to a maximum saturation magnetization (Ms) of 64.1 emu/g at 300 K and 73.5 emu/g at 2 K.