International Journal of Physical Sciences Vol. 7(16), pp. 2713 - 2719, 16 May, 2012 Available online at http://www.academicjournals.org/IJPS DOI: xxx ISSN 1992 - 1950 ©2012 Academic Journals Full Length Research Paper Two step growth process of iron-platinum (FePt) nanoparticles MAJID FARAHMANDJOU Department of Physics, Varamin Pishva Branch, Islamic Azad University, Varamin, Iran. E-mail: farahmandjou@iauvaramin.ac.ir. Tel: +982136725011-14. Fax: +982136724767. PACS: 81.16.Be; 81.16.Dn; 78.67.Bf, 81.07.-b. Accepted 08 May, 2012 In this paper, FePt nanocrystals have been prepared by adding LiBEt3H to the phenyl ether solution of FeCl 2 . 4H 2 O and Pt(acac) 2 precursors in the presence of oleic acid and oleylamine surfactants and 1,2- hexadecanediol as the reducing reagent at 195°C, followed by refluxing at 245°C by sol process. Similarly, Pt nanoparticles were made by adding 1, 2-hexadecanediol as the reducing reagent to the phenyl ether solution of Pt (acac) 2 . The results of Transmission electron microscopy (TEM) images showed that 2 to 7 nm Pt nanoparticles are formed via one step growth whereas, bimetallic 4 nm magnetic FePt nanocryctals are formed by two step growth as core-shell with good uniformity in size and shape. The size measurement results indicated that the standard deviation of FePt nanoparticles improves to 8% because of two step growth process. In order to phase transition from fcc to L1 0 structure , the FePt nanoparticles were annealed at 750°C for 4 h. The structural properties of FePt nanoparticles were analyzed by XRD spectra. To prevent FePt nanoparticles from sintering, NaCl particles were used as the separating media. SEM and TEM observations of FePt show the salt-matrix FePt nanoparticles with size of 40 nm after annealing. Key words: Growth, iron-platinum (FePt) nanoparticles, equilibrium interactions, sol process. INTRODUCTION The study of magnetic nanostructures is attracting much interest from both fundamental and applied point of views (Jia and Misra, 2011). Novel outstanding properties of such nanostructures can be directly correlated to their nanoscale in one or more dimensions (Martin et al., 1999). Chemically synthesized magnetic nanoparticles have drawn much attention (Sun et al., 2000; Chen and Nikles, 2002; Shevchenko et al., 2002) due to the unique magnetic properties derived from small particle sizes and uniform size distribution. Chemical approach is a better way to fulfill this compared with physical ways since particle size, shape and size distribution can be better controlled in chemical synthesis. FePt hard magnetic nanoparticles are of special interest as they may be used for future ultrahigh-density magnetic recording media (Weller et al., 2000) and high performance permanent magnetic nanocomposites (Zeng et al., 2002). Previous work on the synthesis of FePt nanoparticles involved the reduction of Pt (acac) 2 and the decomposition of Fe(CO) 5 (Sun et al., 2001) and other works included addition of Ag, Co to the FePt nanoparticles to improve their physical and magnetic properties (Chen and Nikles, 2002; Kang et al., 2002). Recently, the formation of 4 nm FePt nanoparticles via the simultaneous reduction of FeCl 2 and Pt(acac) 2 as well as Fe and Pt acetylacetonate has also been reported (Sun et al., 2003; Jeyadevan et al., 2003). The systematic adjustment of the reaction parameters, such as reaction time, temperature, concentration, and the selection of reagents and surfactants, can be used to control the size, shape, and quality of nanoparticles. During nanocrystals growth, the surfactants in solution adsorb reversibly to the surfaces of the nanocrystals, providing a dynamic organic shell that stabilizes the nanoparticles in solution and mediates their growth. Surfactants that bind more tightly to the nanoparticle surface or larger molecules providing greater steric hindrance slow the rate of materials addition to the nanoparticle, resulting in smaller average nanoparticle