Nanometer-sized maghemite iron oxide (gamma-Fe2O3) particles were produced first by synthesis of a precursor, gamma-FeO(OH), in a surfactant-less microemulsion and subsequent heat treatment of the gamma-FeO(OH). The precursors and gamma-Fe2O3 powder were characterized using thermogravimetric analysis (TGA), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Susceptometer from Quantum Design (SQUID) measurements. TGA and XRD analysis indicated the formation of single cubic phase when the samples were heat-treated at 240 degreesC. TEM reveals that the gamma-Fe2O3 particles are needle-shaped with an aspect ratio of similar to20; typically 5-10 nm wide and over 150 nm long. It was found that these microemulsion-derived gamma-Fe2O3 nanoneedles possess an intrinsic coercivity of 28 Oe at 300 K and 950 Oe at 2 K. (C) 2003 Elsevier Science Ltd. All rights reserved.