Gold-coated iron (Fe@Au) nanoparticles: Synthesis, characterization, and magnetic field-induced self-assembly

A unique reverse micelle method has been developed to prepare gold-coated i ron (Fe@Au) nanoparticles. XRD, UV/vis, TEM, and magnetic measurements are utilized to characterize the nanocomposites. XRD only gives FCC patterns of gold for the obtained nanoparticles. The absorption band of the Fe@Au coll oid shifts to a longer wavelength and broadens relative to that of the pure gold colloid. TEM results show that the average size of Fe@Au nanoparticle s is about 10 nm, These nanoparticles are self-assembled into chains on mic ron scale under a 0.5 T magnetic field. Magnetic measurements show that the particles are superparamagnetic with a blocking temperature (T-B) of 42 K, At 300 K (above T-B), no coercivity (Hc) and remanence (M-r) is observed i n the magnetization curve, while at 2K (below T-B) He and M, are observed t o be 728 Oe and 4.12 emu/g, respectively, (C) 2001 Academic Press.