Structural and Magnetic Properties of CoPt@Au Core-Shell Nanoparticles Prepared Under Ambient Pressure

Abstract

In this study, cobalt platinum alloy-core/gold-shell (CoPt@Au) nanoparticles are prepared by reverse micelle method under ambient pressure, and investigated by X-ray diffraction, transmission electron microscopy (TEM), ultraviolet-visible absorption spectra, and superconducting quantum interference device (SQUID) analyses. Cobalt platinum alloy (CoPt) nanoparticles are synthesized via chemical assembly, and achieved by reducing 0.1 M aqueous metal salts confined in the polar portions of inverse micelles of cetyltrimethylammonium bromide (CTAB) with borohydride. Gold-coated nanocomposites are prevented CoPt oxidation and allowed the samples to be manipulated without additional precautions to prevent oxidation. X-ray diffraction shows that the pattern of CoPt is hidden under the pattern of gold. TEM image reveals that the core-shell structure is obviously observed and the average size of CoPt@Au nanoparticles is about 6∼7 nm. The absorption band of CoPt@Au nanoparticles shifts to a longer wavelength and broadens relative to that of the pure gold. The results of magnetization for CoPt@Au nanoparticles reveal that they are super-paramagnetic, and the blocking temperatures is 75 K. In addition, there is an weak ferromagnetism observed in the results of magnetization for CoPt@Au nanoparticles under −1000 Oe ∼ 1000 Oe at 5K, and the coercive fields is 20 Oe.