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

Abstract

High coercivity L1 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 L1 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 L1 0 structure formation.

Synthesis of a High-Coercivity FePt–Ag Nanocomposite Magnet via Block Copolymer-Templated Self-Assembly

“…The coercivity of the sample synthesized with Ag was much higher than the reported values for chemically synthesized FePt nanocomposites [19][20][21][22]. This suggests that the increase in the coercivity was caused by the addition of Ag to the FePt nanocrystals and that the grain boundaries of the nonmagnetic Ag metal acted as pinning sites, disrupting magnetic coupling between individual FePt nanocrystallites and hindering domain wall motion at an external magnetic field.…”

“…However, Ag diffusion had little effect on the promotion of this chemical ordering change. We hypothesize that the amount of Ag (13%) was insufficient to promote a change in the chemical ordering [19].…”

“…Fabrication of FePt nanostructures by chemical synthesis is a promising alternative, but achieving high coercivity with chemical synthesis methods has been difficult [19][20][21][22]. The problem has been attributed to the difficulty of controlling nanocomposite structures.…”

Chemical Synthesis of Magnetic Nanoparticles for Permanent Magnet Applications

“…When the Au composition was higher than 14 %, the degree of the ordering was improved with the amount of Au present in the alloy structure, and the maximum H c of 12 kOe was achieved for FePtAu NPs with 32 % Au doping (Figure d). The additive element is not limited to Au, but can be extended to other metals as well, such as Ag and Cu, to realize the A1–L1 0 transition in the organic phase reaction solution.…”

Facile liquid-assisted one-step sintering synthesis of superfine L10-FePt nanoparticles

“…13,14 To achieve a higherordered structure, a third element doping method, with elements such as Cu, Ag, Au and Bi, has been employed to accelerate the L1 0 ordering or promote crystallographic orientation. [15][16][17][18] However, to date, the FePt NPs prepared by the direct wet chemical synthesis route show a partial structural ordering that is not high enough for further applications.…”