Monodisperse FePt Nanoparticles and Ferromagnetic FePt Nanocrystal Superlattices
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J. S. Bradley in Cluster and Colloids G. Schmid Ed. (VCH New York 1994) chap. 6.
One typical synthetic procedure is as follows: under airless condition platinum acetylacetonate (197 mg 0.5 mmol) 1 2-hexadecanediol (390 mg 1.5 mmol) and dioctylether (20 ml) were mixed and heated to 100°C. Oleic acid (0.16 ml 0.5 mmol) oleyl amine (0.17 ml 0.5 mmol) and Fe(CO) 5 (0.13 ml 1 mmol) were added and the mixture was heated to reflux (297°C). The refluxing was continued for 30 min. The heat source was then removed and the reaction mixture was allowed to cool to room temperature. The inert gas protected system could be opened to ambient environment at this point. The black product was precipitated by adding ethanol (∼40 ml) and separated by centrifugation. Yellow-brown supernatant was discarded. The black precipitate was dispersed in hexane (∼25 ml) in the presence of oleic acid (∼0.05 ml) and oleyl amine (∼0.05 ml) and precipitated out by adding ethanol (∼20 ml) and centrifuging. The product was dispersed in hexane (∼20 ml) centrifuged to remove any unsolved precipitation (almost no precipitation was found at this stage) and precipitated out by adding ethanol (∼15 ml) and centrifuging. The materials were redispersed in hexane and stored under N 2 . The total weight of material recovered was 162 mg.
The elemental composition of the as-synthesized FePt particle materials was obtained by inductively coupled plasma–atomic emission spectrometry. The samples were precipitated from hexane dispersions by adding ethanol and then drying. The analysis was performed at Galbraith Laboratories (Knoxville TN).
Although the particle dispersion can be handled without inert gas protection it is advisable to store the hexane dispersion under N 2 for long-term protection.
An example is as follows: 0.02 ml of hexane-dispersed FePt nanoparticles (equivalent to ∼5 mg/ml) was deposited on a SiO 2 /Si substrate (∼0.5 cm by 1 cm). The solvent was allowed to evaporate slowly (∼5 min) at room temperature. The as-deposited thin film was then transferred into a N 2 glove box (O 2 concentration <2 ppm) and annealed in a Thermolyne 1300 furnace. The temperature was raised to 550°C from room temperature over a period of 13 min and maintained for 30 min. The sample was taken out of the furnace and cooled to room temperature in the N 2 box. Composition and thickness of the FePt nanocrystal assembly were determined by Rutherford backscattering spectrometry. This procedure yielded a ∼120-nm-thick FePt nanocrystal assembly.
Powder Diffraction File 43-1359 (International Center for Diffraction Data Newtown Square PA 1994).
We thank J. Bruley and A. Kellock for their help with high-resolution TEM and Rutherford backscattering measurements. D.W. and L.F. gratefully acknowledge support by Advanced Materials Research Institute and the Department of Defense/ Defense Advanced Research Projects Agency through grant MDA 972-97-1-003.