Magnetic Properties and Fabrication of Monodisperse FePd Nanoparticles
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Magnetic Properties and Fabrication of Monodisperse FePd Nanoparticles Yanglong Hou, Hiroshi Kondoh, and Toshiaki Ohta* Department of Chemistry, School of Science, The University of Tokyo, Tokyo 113-0033, Japan Fax: 81-3-38121896; Tel:81-3-58414333; E-mail: [email protected] ABSTRACT The combination of 1-adamantanecarboxylic acid and tri-alkylphosphine was applied to produce monodisperse FePd nanoparticles by the polyol reduction of palladium acetylacetonate and thermally decomposition of iron pentacarbonyl. Images of high resolution transmission electron microscopy (TEM) and X-ray diffraction (XRD) data indicate a highly monodisperse and crystalline nature of the FePd nanoparticles. Magnetic studies performed by Quantum Design SQUID magnetometer show that FePd (16nm) nanoparticles are superparamagnetic at room temperature. INTRODUCTION Physical and chemical properties of nanosized materials are highly dependent on the nanocrystal size, monodispersity, structures and defects [1-3]. The preparation of nanosized materials with a desired size is indispensable to investigate and utilize their size-dependent properties. Therefore, facile and reproducible approaches to prepare monodisperse nanoparticles are much interest [4-6]. Magnetic nanoscale materials have attracted much attention due to their potential applications in magnetic recording devices, medical diagnoses, and magneto-optical system [7, 8]. In the recent development, monodisperse magnetic nanocrystals including FePt, ferrite, Co and Ni etc were obtained by high temperature reduction procedure in the presence of oleic acid, or some combinations of surfactants such as oleic acid-oleylamine, tri-butylphosphine (TBP)- tri-butylphosphine oxide (TBPO) [8-10]. Weller and co-workers reported the fabrication and growth mechanism of high crystalline CoPt3 nanoparticles, in which the combination of 1-adamantanecarboxylic acid (ACA) and hexadecylamine (HDA) were used as the stabilizers [11]. However, these combinations of surfactants introduced above met limited success in the fabrication of FePd nanoparticles [11,12], which is a class of promising material as their high magnetocrystallic anisotropy, Ku=2.6×106 J/m3, [13]. In this paper, we reported that monodisperse FePd nanoparticles have been prepared by reducing Pd(acac)2 (acac = acetylacetonate) with hexadecanediol and decomposing Fe(CO)5 thermally in the presence of novel surfactants combination with ACA-TBP as stabilizers. The self-assembled nanostructures of FePd were also formatted, suggesting high monodispersity of FePd nanoparticles. Note that the use of the combination of ACA and TBP is the key for producing FePd nanoparticles with monodisperse size. EXPERIMENTAL DETAILS TBP and ACA were purchased from Aldrich, other chemicals were from Wako chemicals. All of them were used without further purification. The synthesis of FePd nanoparticles was performed by using standard Schlenk-line technique. In a typical procedure, 0.08g of Pd(acac)2 (0.25mmol), and 0.54g (3mmol) of ACA were dissolved in 1m
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