Magnetic properties of FePtx/Au and CoPtx/Au core-shell nanoparticles

The gold-coated nanocomposites with magnetic core based on the alloys FePt, Fe2Pt, CoPt and CoPt3 were synthesized using the reverse micelles technique. They were characterized using X-ray diffractometry, SQUID magnetometry and electron microscopy (TEM). It was found that the Fe2Pt/Au samples exhibited higher coercivity than FePt/Au, 2885 Oe vs. 500 Oe at 2 K. For the cobalt-based materials, the values of blocking temperature and coercivity increase as the Pt content increases. Annealing of the Co/Au and CoPt3/Au composites at 400 degreesC did not cause any significant change in the magnetic behavior. Annealing of FePt/Au and CoPt/Au samples caused increase of coercivity, H-C = 194 vs. 0 Oe for the former, and H-C = 500 Oe vs. 25 Oe for the later composite at 300 K. We suppose that annealing of both 1 : 1 alloys caused ordering in their cores, that affected their magnetic properties. (C) 2001 Elsevier Science B.V. All rights reserved.