CoPt magnetic nanocrystals in the A1/L10 transformation

CoPt magnetic nanocrystals have been synthesized in a range of size from 2 to 4 nm using a colloidal chemical synthetic method. As-synthesized nanocrystals exhibit an equiatomic composition and a crystalline phase of type alloy CoPt A1 disordered. The morphology and the magnetic properties were investigated for different crystal size. In order to reach the crystalline transition toward the L1(0) ordered phase, a thermal annealing has been carried out on CoPt nanocrystals of 4 nm. We showed that the use of HOPG substrate both limits the coalescence effects and promotes the structural ordering. The modification of the crystalline structure selected area electron diffraction (SAED) and the magnetic properties (superconducting quantum interference device) has been studied for different heat-treatment conditions. Ferromagnetic properties at room temperature were achieved for nanocrystals of 16 nm in average size with a coercivity of 4 kOe. (C) 2011 American Institute of Physics. [doi:10.1063/1.3575333]