Polymer-mediated synthesis of gamma-Fe2O3 nano-particles

Nano-particles of gamma -Fe2O3 were synthesized by reacting polyethylene ox ide-FeCl3 complex with NH4OH. These were characterized by X-ray diffraction (XRD), scanning electron miscroscopy (SEM), selected area electron diffrac tion (SAED) and transmission electron microscopy (TEM). The average particl e size was found to be 10 nm, as determined from the line broadening of the main XRD peak. The crystalline phase was a spinel-type tetragonal structur e, which was confirmed from the electron diffraction pattern. The zero fiel d cooled magnetization of samples with varying gamma -Fe2O3, content as a f unction of temperature was measured using a vibrating sample magnetometer. The magnetization curves show a peak at low temperature (15 K) correspondin g to the blocking temperature T-B. The value of T-B was found to decrease w ith decreasing particle size. The magnetization measurements with respect t o field at 5 and 170 K confirmed the transition from superparamagnetic to s pin-glass state at T-B, as evidenced from the remanence and hysteresis. The se results can be explained on the basis of Ni el's theory of superparamagn etism as applied to nano-particles. (C) 2001 Published by Elsevier Science Ltd.