Improving the ordering and coercivity of L10-FePt nanoparticles by introducing PtAg metastable phase

Abstract

Third element doping can accelerate ordering transformation and directly synthesize L10-FePt nanoparticles (NPs). However, this accelerating effect is limited due to the extremely low migration rate of Fe and Pt atoms. In this work, PtAg metastable phase is first introduced into chemical synthesis. Compared with the normal direct synthesis, the metastable phase method shows a much higher efficiency on promoting ordering transformation, and the FePt NPs present good dispersity, ultra-high ordering and coercivity up to 8600 Oe. The PtAg metastable phase is easy to be decomposed to Ag and Pt. The obtained Ag atoms migrate to surface area of the NPs because of their higher self-diffusion coefficients and the smaller surface energy. Simultaneously, the Fe atoms migrate into the NPs, and form the FePt phase. During the ordering diffusion of atoms, the mobility of Ag is much higher than that of Fe, which can generate a lot of vacancies in the lattice. These vacancies can obviously improve the migration rate of Fe and Pt atoms in the lattice, and powerfully promote ordering diffusion. Therefore, the introduced metastable phase can construct an optimal condition for the disorder-order transformation, and synthesize FePt NPs with highly ordering degree and good dispersity.