J Supercond Nov Magn (2012) 25:2075–2079 DOI 10.1007/s10948-012-1586-1 ORIGINAL PAPER Effect of Oleic Acid and Oleylamine Surfactants on the Size of FePt Nanoparticles Majid Farahmandjou Received: 6 February 2012 / Accepted: 5 April 2012 / Published online: 27 April 2012 © Springer Science+Business Media, LLC 2012 Abstract FePt magnetic nanoparticles have been synthe- sized by superhydride reduction of FeCl 2 and Pt(acac) 2 at high temperature. Adding superhydride (LiBEt3H) to the phenyl ether solution of FeCl 2 and Pt(acac) 2 in the presence of oleic acid, oleylamine, and 1,2-hexadecanediol at 190 ◦ C, followed by refluxing at 245 ◦ C, led to monodisperse 3.5 nm FePt nanoparticles. The effect of oleylamine and oleic acid surfactants on the nucleation and growth of FePt nanopar- ticles were studied. The size of Pt was controlled by oley- lamine surfactant in nucleation stage. To prevent sintering of the FePt nanoparticles, oleic acid surfactant was used in growth stage. The energy dispersive spectroscopy results re- vealed that the particle composition was first Fe 11 Pt 89 in nucleation stage and after adding superhydride the compo- sition changed to Fe 63 Pt 37 in growth stage. The structural and magnetic measurements indicated that the L1 0 structure of FePt nanoparticles is formed after annealing and the coer- civity of superlattice FePt nanoparticles increases to 7.5 kOe after heat treatments. Keywords Aggregation · FePt Nanoparticles · Growth · Nucleation · Surfactant 1 Introduction FePt nanoparticles have great application potential in ad- vanced magnetic materials such as ultrahigh-density record- ing media and high-performance permanent magnets [1–3]. M. Farahmandjou ( ) Department of Physics, Varamin Pishva Branch, Islamic Azad University, Varamin 7489-33817, Iran e-mail: farahmandjou@iauvaramin.ac.ir M. Farahmandjou e-mail: farahmand_ph@yahoo.com The key for applications is the very high uniaxial mag- netocrystalline anisotropy of the L1 0 -FePt phase which is based on crystalline ordering of the face-centered tetragonal (fct) structure [4]. Synthesis of magnetic nanoparticles has long been of sci- entific and technological interest due to their potential ap- plications in tissue imaging [5] drug delivery [6] and in- formation storage [7]. Important progress has been made in chemical synthesis of monodisperse magnetic nanoparti- cles of metals [9], alloys [8], and oxides [10]. The chemical growth of bulk or nanometer-sized materials inevitably in- volves the process of precipitation of a solid phase from so- lution. A good understanding of the process and parameters controlling the precipitation helps to improve the engineer- ing of the growth of nanoparticles to the desired size and shape. For a particular solvent, there is certain solubility for a solute, whereby addition of any excess solute will result in precipitation and formation of nanocrystals. Thus, in the case of nanoparticle formation, for nucleation to occur, the solution must be supersaturated either by directly dissolving the solute at higher temperature and then cooling to low tem- peratures or by adding the necessary reactants to produce a supersaturated solution during the reaction [11, 12]. The precipitation process then basically consists of a nucleation step followed by particle growth stages [13, 14]. Uniformity of the size distribution is achieved through a short nucle- ation period that generates all of the particles obtained at the end of the reaction followed by a self-sharpening growth process. If the time of nanocrystal growth during the nu- cleation period is short compared to the subsequent growth processes, the nanocrystals can become more uniform over time as size focusing takes place [15–17]. During nanocrys- tal growth, the surfactants in solution adsorb reversibly to the surfaces of the nanocrystals, providing a dynamic or- ganic shell that stabilizes the nanocrystals in solution and