In this work we present the magnetic properties of gold coated FePtnanoparticles and the study of stable aqueous dispersions of FePt@Au and FePtsynthesized after ligand exchange with mercaptoundecanoic acid. The particlesize determined from TEM micrographs goes from 4 nm for the uncoatednanoparticles to a maximum of 10 nm for the gold coated ones indicating thatthe thickness of the shell ranges from 1 to 3 nm. The magnetic characterizationconsists in hysteresis cycles at 10 and 300 K. The results show that, at lowfield and room temperature, the magnetic behavior of uncoated and coatednanoparticles are surprisingly quite similar. Since the gold coatednanoparticles keep the magnetic properties of FePt and the presence of goldimproves the functionalization of nanoparticles, the system is suitable forbiological application. Mercaptoundecanoic ligand transfer was used to renderwater stable nanoparticles in a wide pH range. Transmission electron microscopyand dynamic light scattering results show the nanoparticles slightlyagglomerate after ligand exchange. Fourier transform infrared spectroscopyresults suggest that thiol bind to the gold atoms of the surface.
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