Original Research Paper Laser synthesis of magnetic iron–carbon nanocomposites with size dependent properties I. Morjan a , F. Dumitrache a , R. Alexandrescu a,⇑ , C. Fleaca a , R. Birjega a , C.R. Luculescu a , I. Soare a , E. Dutu a , G. Filoti b , V. Kuncser b , G. Prodan c , N.C. Popa d , L. Vékás d a National Institute for Lasers, Plasma and Radiation Physics, P.O. Box MG-36, 077125 Bucharest, Romania b National Institute of Materials Physics, P.O. Box MG-07, 077125 Bucharest-Magurele, Romania c Ovidius University of Constanta, Constanta, Romania d Center for Fundamental and Advanced Technical Research, Romanian Academy-Timisoara Division, Timisoara, Romania article info Article history: Received 4 August 2010 Received in revised form 4 November 2010 Accepted 22 December 2010 Available online 4 January 2011 Keywords: Iron–carbon nanocomposites Laser pyrolysis Core–shell nanoparticles Particle size distribution Magnetic Mössbauer spectroscopy abstract Iron–carbon nanocomposites have gained interest due to their new engineering and biomedical applica- tions. Carbon coated iron nanoparticles (Fe@C) were obtained continuously and in a single step using the laser pyrolysis method. The continuous wave CO 2 laser beam was used to continuously heat a sensitized (with ethylene) precursor gas mixture, in which iron pentacarbonyl (vapor) and acetylene were the iron and carbon donors, respectively. The effect of varying the residence time in the reaction zone through the variation of the internal nozzle diameter was explored in order to improve the particle size and the phase distributions. At increased nozzle diameter, (i) the particle mean diameter increases (from about 3.5 to 10.5 nm), (ii) higher ordering of the crystallographic network seems to occur, (iii) the dominance of the a-Fe and iron carbide phases is revealed. Onion-like graphenic layers often cover the buried iron cores. Magnetic measurements and temperature dependent Mössbauer spectroscopy were used in order to find correlations concerning the magnetic behavior and the Fe phase composition of samples. Prelimin- ary experiments for obtaining stable water-based magnetic nanofluids are discussed. Ó 2011 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved. 1. Introduction Due to their multi-functionality, new types of composite core– shell nanostructures present high interest for the design of efficient technological applications. For preparing composite inorganic/car- bon core–shell nanostructures, a variety of inorganic cores have been used, including metals (Fe, Co, Ni [1,2], Ag [3]), iron carbide [4], SiC [5], Te [6], copper sulfide [7]. However, because of the widespread applications of magnetic nanoparticles in biomedical, biotechnology, engineering, material science and environmental areas, carbon encapsulated iron based nanoparticles are inten- sively studied [8,9]. Dispersions with functionalized iron based nanoparticles have biomedical applications as magnetic carriers for drug delivery and contrast agent [10,11]. The incorporation of iron nanoparticles into a carbonaceous matrix could ease the trans- portation, storage and use of these materials by preventing the oxidation [11]. Furthermore, the nonmagnetic carbon shell mini- mizes the magnetic interactions between the iron cores and thus the nanocomposite material acts as a group of isolated non-inter- acting single magnetic domains [12]. It was recently shown that the magnetic properties of carbon-coated nanoalloy cores e.g. NiRu may be tailored through the synthesis parameters [13]. Such nanomaterials could exhibit unusual effects: anomalous mag- neto-resistance, a large magneto-caloric effect, etc. The possibility to control the size and structure of nanoparticles permits one to produce nanocomposites with specified magnetic properties [14]. In previous work [15] we have employed the laser pyrolysis technique for the preparation of carbon coated iron nanoparticles using iron pentacarbonyl as iron donor. This one-step synthesis technique combines the fast heating of gas phase processes with the sudden quenching of reaction products. Ethylene/acetylene mixtures [15] or toluene [16] were used as carbon precursors. In the present work we have refined the synthesis technique in order to further demonstrate the possibility to vary the chemical content and the nanoparticle dimensions. We report the successful control of the structural and magnetic properties of Fe@C nanocomposites by essentially varying the nozzle diameter of the emergent reactive gas flow. The magnetic properties and the Fe phase composition of 0921-8831/$ - see front matter Ó 2011 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved. doi:10.1016/j.apt.2010.12.014 ⇑ Corresponding author. Address: Laboratory of Laser Photochemistry, National Institute for Lasers, Plasma and Radiation Physics, P.O. Box MG-36, R-76900 Bucharest, Romania. Tel.: +40 21 457 44 89; fax: +40 21 457 42 43. E-mail addresses: rodica.alexandrescu@inflpr.ro, ralexandrescu2001@yahoo. co.uk (R. Alexandrescu). Advanced Powder Technology 23 (2012) 88–96 Contents lists available at ScienceDirect Advanced Powder Technology journal homepage: www.elsevier.com/locate/apt