Order-disorder investigation of hard magnetic nanostructured FePt alloy

Well dispersed FePt nanoparticles are synthesized by the reduction of platinum (II) acetylacetonate and iron (III) acetylacetonate in the presence of oleic acid and oleylamine as a surfactant. Detailed investigations on the correlation between the magnetic and structural properties of these nanoparticles are presented as a function of annealing temperature. Transmission electron microscopy shows well dispersed nanoparticles with an average size of 4 nm. The phase of FePt nanoparticles has been studied using selected area electron diffraction which shows the clear transition from disordered face centre cubic (DFCC) to ordered face centre tetragonal (OFCT) at 750 degrees C. The x-ray diffraction as well as the magnetic measurements confirms the complete transformation from DFCC to OFCT phase at 750 degrees C with initiation of ordering at 500 degrees C. The magnetic measurements at room temperature show a single phase hysteresis loop at 750 degrees C with a coercivity of H-c similar to 11.8 kOe.