a-Fe nanoparticles produced by laser ablation: Optical and magnetic properties Yosmery Vitta a , Vincent Piscitelli a , Alberto Fernandez a , Fernando Gonzalez-Jimenez b , Jimmy Castillo a,⇑ a Laboratorio de Espectroscopia Laser, Facultad de Ciencias, Universidad Central de Venezuela, Caracas 47102, 1020a, Venezuela b Laboratorio de Magnetismo, Esc. De Fisica, Facultad de Ciencias, UCV, Caracas 47586, 1041a, Venezuela article info Article history: Received 4 February 2011 In final form 4 July 2011 Available online 13 July 2011 abstract Nanoparticles with optical and magnetic responses are of great applicability in different fields. In this work, zero valent iron nanoparticles were prepared by laser ablation and stabilized in a surfactant solu- tion to keep particles dispersed and protected in the solution. Optical and magnetic properties of nano- particles were measured, by UV and Mössbauer spectroscopy. The results show the formation of nanoparticles of a-Fe (ferromagnetic). Our method of preparation, which uses a high H + concentration in the medium, diminishes the zero valent iron oxidation, producing iron nanoparticle with a core of a-Fe and a small shell probably composed of iron oxides. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction Magnetic nanoparticles (MNPs) have shown great potential in biomedical applications such as magnetic separation, magnetic resonance imaging (MRI), targeted drug delivery, and hyperther- mia treatment of cancer. In particular, MNPs are excellent MRI con- trast agents for cellular and molecular imaging. MNPs composed of Fe 3 O 4 have been extensively investigated due to their excellent magnetic properties and biocompatibility. Synthesis of metallic iron nanoparticles and their dispersion in various liquid media is of great interest in the field of nano-mag- netic materials. Alpha iron (a-Fe) is a class of ferromagnetic mate- rial with high magnetic moment density (218 emu/g or 1713 emu/ cc) and is magnetically soft. It has been reported to show super- paramagnetic behavior for a-Fe nanoparticles in the size range be- low 20 nm [1,2], and its stable dispersions show high magnetic moment and are predicted to have important applications in bio- separation, biosensing, drug delivery and MRI contrast enhance- ment [3,4]. Procedures leading to monodisperse Fe nanoparticles are well documented [5]. The most common chemical methods used for the preparations include thermal decomposition of iron pentacarbonyl (Fe(Co) 5 ) [5–11], reductive decomposition of iron (II) bis(trimethylsilyl)amide (Fe[NSi(CH 3 ) 3 ] 2 ) [12] and reduction of iron (III) acetylacetonate (Fe(acac) 3 ) or other iron salts [13]. Although the size of the particles is well controlled, the syntheses reveal that the particles so prepared are extremely reactive and subject to easy oxidation, giving various iron oxide nanoparticles. As a result, the production of stable a-Fe nanoparticle dispersions, especially aqueous dispersions for potential biomedical applica- tions is not easy to achieve via wet synthesis [1]. Recently, pulsed laser ablation of metal targets in liquid media has attracted great interest [14], because such laser ablation in li- quid (LAL) can produce the extreme conditions of pressure and temperature to lead to formation of metastable nanostructures and hence novel properties. When a pulsed laser beam with en- ough energy irradiates on a metal target in a transparent liquid, a local plasma, at a super high temperature (about 6000 K) and high pressure (about 1 Gpa), will instantly be produced on the so- lid–liquid interface and quenched quickly after one pulse due to adiabatic expansion of the plasma and its interaction with the sur- rounding media. The whole process is finished in about 1 ls. So, the laser ablation of metal targets in liquid media can form some special nanostructures, which cannot be obtained by the conven- tional methods. In the following work we present a laser ablation methodology for obtaining a-Fe nanoparticles. The nanoparticles were prepared and stabilized in a surfactant solution to keep particles dispersed and protected in the solution. Optical and magnetic properties of the nanoparticles were measured, by UV and Mössbauer spectros- copy. The results show the formation of nanoparticles of a-Fe (fer- romagnetic), these surfactant-stabilized particles are protected from oxidation by surface passivation which maintains the mag- netic state for periods longer than 1 month. 2. Materials and methods 2.1. Chemicals Analytical grade ethanol and deionized water 18 mX were used as solvents. A 0.045 l M surfactant solution was prepared by dis- solving the appropriate amount of sodium dodecyl sulfate (SDS) (ScharlauChemie, Barcelona, España) in a methanol–water 0009-2614/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2011.07.020 ⇑ Corresponding author. E-mail address: jimmy.castillo@ciens.ucv.ve (J. Castillo). Chemical Physics Letters 512 (2011) 96–98 Contents lists available at ScienceDirect Chemical Physics Letters journal homepage: www.elsevier.com/locate/cplett