One-Step Synthesis of High-Coercivity L1₀-FePtAg Nanoparticles: Effects of Ag on the Morphology and Chemical Ordering of FePt Nanoparticles

High coercivity L 1 0 -ordered (FePt) 1– x Ag x nanoparticles (NPs) were directly synthesized using a one-step solution method without post-thermal annealing. The effect of silver additive on the morphology, chemical ordering, and magnetic properties of FePt NPs was studied. Magnetic measurements showed that the FePt NPs without Ag additive were soft magnetic with a coercivity of 300 Oe, whereas a record coercivity of 7600 Oe was obtained when the molar ratio of Ag reached 29% in FePtAg. High-resolution transmission electron microscopy and X-ray diffraction analyses proved that Ag atoms in the L 1 0 -phase FePtAg NPs were segregated on the surface of the particles, which revealed that the diffusion of Ag atoms out of the FePt grains is the major driving force behind the L 1 0 structure formation.