Reduction of Sintering during Annealing of FePt Nanoparticles Coated with Iron Oxide

FePt/iron oxide core/shell nanoparticles are synthesized by a two step polyol process with 1,2-hexadecanediol as the reducing reagent. Monodispersed 2.6-nm FePt nanoparticles are first obtained by reduction of iron(III) acetylacetonate and platinum(II) acetylacetonate. These preformed FePt nanoparticles are then used as seeds and an iron oxide shell is formed in the second synthesis step. The role of the iron oxide shell on sintering of FePt nanoparticles is investigated. Annealing studies show that these FePt/iron oxide core/shell structures are stable after annealing at 550 °C for 30 min at which 2.6-nm FePt nanoparticles without oxide shell coating start to sinter. Low-temperature magnetic hysteresis behavior of the annealed core/shell nanoparticles suggests exchange coupling between the magnetically hard FePt core and the magnetically soft iron oxide shell.