Synthesis and magnetic properties of CoPt nanoparticles

High magnetocrystalline anisotropy CoPt particles with an average size of 8 nm were synthesized by the superhydride reduction of CoCl2 and Pt(acac)(2) at a high temperature. As-made particles showed a disordered face-centered cubic lattice and were superparamagnetic. Upon heat treatment at temperatures above 600 degreesC, the particles transformed to the L1(0) phase, as indicated by the appearance of the superlattice peaks in the x-ray diffraction and high magnetocrystalline anisotropy. The temperature dependence of the coercivity of nanoparticles annealed at 650 degreesC was measured from 10 to 300 K and analyzed using a Sharrock formula. After annealing at 650 degreesC, the anisotropy of the nanoparticles was Ksimilar to1.7x10(7) erg/cm(3). (C) 2004 American Institute of Physics.