Journal of Magnetism and Magnetic Materials 316 (2007) e169–e172 Ordering kinetics of chemically synthesized FePt nanoparticles I. Zafiropoulou à , V. Tzitzios, N. Boukos, D. Niarchos à Institute of Materials Science, National Center for Scientific Research ‘‘Demokritos’’, Ag. Paraskevi 15310, Athens, Greece Available online 28 February 2007 Abstract FePt is a very interesting magnetic material and many attempts have been made towards the lowering of its ordering temperature. Addition of Au and Ag seems to be a satisfying solution, since it can reduce the annealing temperature by 100–150 1C. In the present work, FePtAu and FePtAg nanoparticles have been synthesized via a modification of the polyol method in different compositions. The ideal percentage of the third metal was chosen in order to study its effect on the transformation to the L1 0 phase. Some attempts have been made to study the ordering kinetics and the role of the third metal. r 2007 Elsevier B.V. All rights reserved. PACS: 75.50.Tt; 75.50.Vv; 75.50.Ss Keywords: FePt; FePtAu; FePtAg; Magnetic nanoparticles; L1 0 transformation 1. Introduction FePt appears as an interesting material for various applications with ultra high density recording media being the most popular. This material displays high magneto- crystalline anisotropy ðK u 6:6–10  10 6 Jm 3  Þ resulting in high value of coercivity, and at the same time stability of the magnetization against thermal fluctuation and demag- netizing effects. Nevertheless, there is a number of problems that have to be overcome, like the high temperature annealing required to obtain the hard magnetic L1 0 phase which simultaneously causes nanopar- ticles aggregation resulting to larger particles with broad size distribution. Addition of a third metal (mainly Au and Ag) can deal with this problem, since Au and Ag enhances the phase transformation lowering the ordering temperature [1]. Lately, chemical synthesis procedures are mainly used to produce such nanocrystalline materials, since these procedures offer the opportunity to control the product’s morphology and properties altering the reaction conditions. Polyol method [2] was firstly developed for the synthesis of FePt nanoparticles and since then it has been extensively used for various materials. In the present study, a modification of the above method has been applied, which uses commercially available and low cost reagents [3]. FePtAu and FePtAg have been synthesized in various compositions and the role of the third metal along with its effect on the transformation kinetics has been studied. 2. Experimental The synthesis method of the FePt, FePtAu and FePtAg nanoparticles, which is a modification of the polyol method, is based on the thermolytic reduction of metal salts in a high boiling point solvent, in the presence of a mild reducing agent and surfactants. The metal precursors used are Fe(acac) 3 , Pt(acac) 2 , AuCl 3 and AgNO 3 , in the appropriate quantities in order to synthesize trimetallic materials with 7%, 13% and 19% of the third metal, while the molar ratio of Fe/Pt was constantly kept equal to 1/1. The detailed synthetic procedure for FePt nanoparticles is described elsewhere [3]. In this case, the third metal was added in the reaction solution along with the Fe and Pt precursors. The samples were annealed in a tube furnace, under reducing atmosphere (4% H 2 Þ for 1 h at tempera- tures ranging from 300 to 550 1C. A D 500 Siemens diffractometer, with CuK a radiation (l ¼ 1:5418 A) was used for the structure study, while the ARTICLE IN PRESS www.elsevier.com/locate/jmmm 0304-8853/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2007.02.072 à Corresponding authors. Tel.: +30 210 650 3385; fax: +30 210 651 9430. E-mail addresses: zafeirini@ims.demokritos.gr (I. Zafiropoulou), dniarchos@ims.demokritos.gr (D. Niarchos).