Size and Shape Control of Monodisperse FePt Nanoparticles

Abstract

Morphological control of FePt nanoparticles has been systematically studied. By varying synthetic parameters including precursors, solvents, amount of surfactants, and heating rate of the solution, the particle size from 2 to 9 nm can be tuned with 1 nm accuracy. While most particles are spherical in shape, cubic particles can be obtained when particles are greater than 7 nm. Rod-shape nanoparticles have also been obtained. The as-synthesized nanoparticles are found to be superparamagnetic at room temperature and their blocking temperature is size dependent that increases with particle size. After annealing in a reducing atmosphere, the nanoparticles form hard magnetic films with ordered fct structure and high coercivity up to 2.7 T.

Prospects for nanoparticle-based permanent magnets

“…Wet-chemical techniques are suitable for producing monodisperse and self-assembled nanoparticles of average sizes tunable from 3 to 15 nm, which are generally produced by the reduction or decomposition of metal salts in the presence of stabilizing or capping agents [9,10,[20][21][22][23]. For example, the reduction of platinum acetylacetonate and decomposition of iron pentacarbonyl in the presence of oleic acid and oleylamine stabilizers results in monodisperse FePt nanoparticles [9], which can be deposited as self-assembled nanoparticle arrays on suitable substrates using spin or dip-coating.…”

Shape control of FePt nanocrystals

“…3 Typically, when a smaller amount of surfactants is injected simultaneously after the addition of Fe͑CO͒ 5 in the ether solvent, spherical FePt nanoparticles are formed. 7,[11][12][13] It has been found from our study that not only the molar ratio of surfactants but also the sequence of addition of the surfactants and metal precursors has influence on the shape of FePt nanoparticles. For example, nanorods and nanowires were obtained when oleylamine was added before the addition of Fe͑CO͒ 5 , followed by oleic acid, at the molar ratio of oleylamine to oleic acid at 4:1͓Figs.…”

“…It is known that surfactants play a vital role in growth of nanocrystals. 3,7,9,[11][12][13][14] The anisotropic interaction between the capping agents and the different facets of Fe-Pt crystals should be the key for the formation of differently shaped nanocrystals. 3 Typically, when a smaller amount of surfactants is injected simultaneously after the addition of Fe͑CO͒ 5 in the ether solvent, spherical FePt nanoparticles are formed.…”

“…[7][8][9][10] Recent progress in chemical synthesis techniques for preparing FePt nanoparticles has shown a great deal of success in tuning particle size while maintaining a narrow size distribution. [11][12][13] Progress has also been made in controlling shape of FePt nanoparticles, including preparation of one-dimensional structures such as nanorods and nanowires. [14][15][16] We recently reported that simultaneous reduction in platinum acetylacetonate ͓Pt͑acac͒ 2 ͔ and iron pentacarbonyl ͑Fe͑CO͒ 5 ͒ in the presence of 1,2-hexadecanediol ͑HDD͒, oleylamine, and oleic acid in a high-boiling ether solvent leads to the formation of FePt nanorods and nanowires.…”

Rapid thermal annealing of FePt nanoparticles

“…The cubic shape may also be explained by the molecular structure of the solvent. 20 The black particles were precipitated after adding 35 ml of ethanol and separated by centrifugation at 6000 rpm for 20 min. The precipitated particles were then dispersed in 10 ml of hexane.…”