We compare ultrathin Fe films grown epitaxially at 50 degreesC on GaAs(0 0 1) substrates having different surface reconstructions in a film thickness range of 2.5-140 monolayers (ML). The surface reconstruction-dependent nucleation of the Fe films was characterized by azimuthal reflection high-energy electron diffraction (RHEED) scans. The Fe/GaAs interface is more abrupt for Fe growth on As-terminated GaAs(0 0 1) templates than on Ga-terminated ones. Our studies of the magnetic properties of the Fe films show that the strong uniaxial anisotropy with the easy axis of magnetization along [1 1 0] is not directly related to the specific GaAs(0 0 1) surface reconstruction. The onset of ferromagnetism in our Fe films starts at 3.5 ML at room temperature. This is only slightly larger than that for Fe films grown on metallic single crystal substrates. The saturation magnetization for Fe films above 4 ML thickness is very close to the bulk value of Fe indicating the absence of interfacial Fe-Ga-As compounds. Fe films with smaller thickness show a reduced magnetic moment which we ascribe to the unfinished coalescence process of Fe islands at the initial stage of growth in agreement with RHEED results. (C) 2004 Elsevier B.V. All rights reserved.