Monodisperse FePt nanoparticles with average size of 2.4 nm were successfully synthesized via chemical co-reduction of iron acetylacetonate, Fe(acac)3, and platinum acetylacetonate, Pt(acac)2, by 1,2-hexadecanediol as a reducing agent and oleic acid and oleyl amine as surfactant. Then using the seed mediated growth process smaller sized FePt nanoparticles are used as seeds for the growth of larger sized FePt particles and there is no specific limitation to achieve upper size range by this method. In this work, we could synthesize FePt nanoparticles up to 4.0 nm. Monodispersity with relatively narrow size distribution and having the same elemental composition with the atomic percentage of Fe x Pt100−x (x = 63) are the main advantages of this method. As-made FePt nanoparticles have the chemical disordered face centered cubic structure with superparamagnetic behavior at room temperature. After annealing these particles become ferromagnetic with high magnetocrystalline anisotropy and their coercivity increases with increasing particle sizes and reaches a maximum value of 5,200 Oe for size of 46.5 nm

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