Abstract: CoFe/Au nanoparticles were prepared by reverse micelle method in the n-hexane solution of sodium bis (2-ethylhexyl)sulfosuccinate (AOT).The CoFe/Au nanoparticles of different size were separated after ligand exchange was fulfilled and AOT was removed by washing of water.The nanoparticles were characterized by ultraviolet visible spectroscopy (UV-Vis),transmission electron microscopy (TEM),X-ray diffraction (XRD),energy dispersive X-ray absorption (EDX) and plasma-atomic emission spectrometry (ICP),respectively.The magnetic properties of CoFe/Au nanoparticles were measured on Superconducting quantum interference device (SQUID).The results indicated that the size of nanoparticles was ca.4 nm and the nanoparticles had very good stability and monodispersity.When a 1.59×10⁴ A/m field was applied,the blocking temperature of CoFe/Au nanoparticles T_b was 65 K.The particles were superparamagnetic above T_b,while the particles were ferromagnetic below T_b with Hc (4.67×10⁴ A/m) at 5 K.

Key words: reverse micelles, ligand exchange, CoFe/Au nanoparticles, magnetic properties