Controlled Synthesis and Assembly of FePt Nanoparticles

Abstract

Monodisperse 4 nm FePt magnetic nanoparticles were synthesized by superhydride reduction of FeCl2 and Pt(acac)2 at high temperature, and thin assemblies of FePt nanoparticles with controlled thickness were formed via polymer mediated self-assembly. Adding superhydride (LiBEt3H) to the phenyl ether solution of FeCl2 and Pt(acac)2 in the presence of oleic acid, oleylamine, and 1,2-hexadecanediol at 200 °C, followed by refluxing at 263 °C, led to monodisperse 4 nm FePt nanoparticles. The initial molar ratio of the metal precursors was retained during the synthesis, and the final FePt composition of the particles was readily tuned. Alternately, adsorbing a layer of polyethylenimine (PEI) and the FePt nanoparticles onto a solid substrate resulted in nanoparticle assemblies with tunable thickness. Chemical analysis of the assemblies revealed that more iron oxide was present in the thinner assemblies annealed at lower temperature or for shorter time. Thermal annealing induced the internal particle structure change from chemically disordered fcc to chemically ordered fct and transformed the thin assembly from superparamagnetic to ferromagnetic. This controlled synthesis and assembly can be used to fabricate FePt nanoparticle-based functional devices for future nanomagnetic applications.

Temperature dependence and magnetocrystalline anisotropy studies of self-assembled L10-Fe55Pt45 ferromagnetic nanocrystals

“…1, 3 Recently, there has been much attention placed on the chemical synthesis of self-assembled, monodispersed, and chemically ordered L1 0 ͑tetragonal phase͒ FePt nanoparticles for future ultrahigh-density magnetic storage. [4][5][6][7][8] In fact, recent advances in magnetic recording technology have indicated that, if self-assembled in a tightly packed, exchangedecoupled array with controlled magnetic easy axis direction, these FePt nanoparticles could support high-density magnetization reversal transitions and would be a candidate for future ultrahigh-density data storage media [8][9][10] with potentially one bit per particle corresponding to storage densities of 20 Tbit/ in. 2 The tetragonal phase of an FePt system is of particular interest because of the high magnetocrystalline anisotropy ͓K U ϳ͑6.6− 10͒ ϫ 10 7 erg/ cm 3 ͔ that should allow the use of smaller particles, but yet avoid thermal instabilities that give rise to superparamagnetic ͑SPM͒ behavior.…”

Microstructures and magnetic alignment of L10 FePt nanoparticles

“…1 Following the seminal work of Sun and coworkers at IBM, much attention has been paid to selfassembled and monodispersed L1 0 FePt and CoPt nanoparticles for future ultrahigh-density magnetic data storage media. [2][3][4][5][6][7] These nanoparticles are very small ͑Ͻ10 nm͒, with uniform grain size and the ability to self-assemble into a regular array. The chemically ordered L1 0 phase of the FePt system is of particular interest because of its high magnetocrystalline anisotropy energy density at the equiatomic composition that should allow the use of smaller, thermally stable magnetic grains and potentially lead to dramatic increases in storage density.…”

Ultrafine FePt Nanoparticles Prepared by the Chemical Reduction Method

“…2,7 Recently, the formation of FePt nanoparticles via the simultaneous reduction of FeCl 2 and Pt(acac) 2 as well as Fe and Pt acetylacetonate has also been reported. 8,9 Particle size produced by the above-mentioned methods is generally around 3-4 nm.…”