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Silver iron oxide nanoparticles of fairly small size (average diameter approximately 1 nm) with narrow size distribution have been synthesized by the interaction of colloidal beta- Fe2O3 and silver nanoparticles. The surface morphology and size of these particles have been analyzed by using atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Their structural analysis has been carried out by employing x-ray diffraction (XRD), selected-area electron diffraction (SAED), optical and infrared (IR) spectroscopic techniques. The ageing of these particles exhibits the formation of self-assembly, possibly involving weak supramolecular interactions between Ag(I)O4 and Fe(III)O4 species. These particles display the onset of absorption in the near-infrared region and have higher absorption coefficient in the visible range compared to that of its precursors. Magnetic measurements reveal an interesting transition in their magnetic behavior from diamagnetic to superparamagnetic. The magnetic moment of these particles attains a limiting value of about 0.19 emu cm(-2), which is more than two times higher than that of colloidal beta- Fe2O3. With enhanced optical and magnetic properties, this system is suggested to have possible applications in optoelectronic and magnetic devices.

β-Fe2O3 nanostructures of different shapes have been synthesized by the hydrolysis of FeCl3 in the absence and presence of Co2+ ions. These materials have been characterized by UV–vis spectroscopy, x-ray diffraction, field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), transmission electron microscopy (TEM) and superconducting quantum interference device magnetometry (SQUID). The addition of Co2+ transforms the shape of nanosized β-Fe2O3 from rods to become spherical. These nanostructures demonstrate superparamagnetic behavior. The extent of saturation magnetization is enhanced by a factor of 3 from 0.49 to 1.56 emu g−1 upon addition of 0.12% Co2+.