Effects of annealing temperature on the structure and magnetic properties of the L10-FePt nanoparticles synthesized by the modified sol–gel method

The ordered face-centered tetragonal (FCT) FePt nanoparticles (NPs) were successfully synthesized by the modified sol–gel method. The relationship between the annealing temperature (400, 500, 600 and 700 °C) and the structure and magnetic properties of the FePt NPs was discussed. And the possible growth mechanism was given in terms of atomic diffusion. Differential thermal analysis (DTA) showed the dehydration of various water molecules and combustion/decomposition of organic groups at the temperature below 600 °C. The X-ray diffraction (XRD) patterns revealed that as the annealing temperature increased to 500 °C, the L10 FePt NPs were formed as was indicated by the appearance of superlattice peaks (001) and (110). Moreover, based on the XRD results, we found that the chemical order parameter S increased with the increase of the annealing temperature. The transmission electron microscope (TEM) images showed that the NPs produced at 700 °C had a mean diameter of 14 nm. The selected area electron diffraction (SAED) patterns of the samples annealed at 700 °C further demonstrated the synthesis of the L10 FePt NPs. The energy dispersive X-ray spectroscopy (EDS) analysis showed that no impurity phases existed in FePt NPs. The maximum coercivity (10,148 Oe) was obtained for the sample annealed at 700 °C.