A novel approach to the synthesis of CoPt magnetic nanoparticles

L1 0 CoPt nanoparticles with face-centred tetragonal (FCT) structure are synthesized by the sol–gel method. Differential thermal analyses show the dehydration of various water molecules and decomposition/combustion of organic groups at a temperature below 600 °C and melting of Co and Pt at 700 °C. X-ray diffraction results show a transition from face-centred cubic to the FCT phase and an increase in particle size with increasing temperature. Transmission electron microscope (TEM) images show that highly monodisperse particles are obtained. High-resolution TEM (HRTEM) images reveal the appearance of L1 0 ordered phase at temperatures above 600 °C. The survey scans of x-ray photoelectron spectroscopy show that no magnetic impurity is detected within the detection limit. The maximum coercivity (353 344 A m −1 ) is obtained for the samples heated at 800 °C. The relationship between the temperature and the structure is discussed and the possible growth mechanism is given in terms of atomic diffusion.