Fe/Au nanoparticles have been chemically synthesized through a reverse micelle reaction and investigated by both conventional and synchrotron-based X-ray diffraction and by magnetic and Mössbauer spectral studies. The powder X-ray diffraction patterns reveal both the presence of crystalline α-iron and gold and the absence of any crystalline iron oxides or other crystalline products. First-order reversal curves, along with the major hysteresis loops of the Fe/Au nanoparticles, have been measured as a function of time in order to investigate the evolution of their magnetic properties. The iron-57 Mössbauer spectra of both uncoated iron nanoparticles and the Fe/Au nanoparticles have been measured at 78 and 295 K and indicate that two major iron-containing components are present, namely, the expected α-iron and the unexpected amorphous Fe 1-xB x alloy; several poorly crystallized ordered iron(III) oxide components as well as paramagnetic iron(II) and iron(III) components are also observed. These results indicate that the Fe-core/Au-shell nanoparticles synthesized through reverse micelles are far more complex than had been believed. © 2006 American Chemical Society.