One-pot synthesis of high magnetization air-stable FeCo nanoparticles by modified polyol method Mohamed Abbas a , Md. Nazrul Islam a , B. Parvatheeswara Rao b , Tomoyuki Ogawa c , Migaku Takahashi a,c , CheolGi Kim a,n a Center for NanoBioEngineering and Spintronics, Department of Materials Science and Engineering, Chungnam National University, Daejeon 305-764, Korea b Department of Physics, Andhra University, Visakhapatnam 530003, India c New industry Creation Hatchery Center, Tohoku University, Aoba-yama 10, Sendai 980-8579, Japan article info Article history: Received 19 July 2012 Accepted 6 October 2012 Available online 13 October 2012 Keywords: Different composition High moment FeCo nanoparticles Polyol process abstract High magnetization FeCo nanoparticles with different Fe/Co ratios have been successfully synthesized by surfactant free simple modified polyol method. Polyethylene glycol (PEG) was used as solvent and reducing agent simultaneously in this synthesis process. All the synthesized samples of FeCo nanoparticles were annealed at 600 1C before characterizations. X-ray diffraction (XRD) data on the samples confirm formation of a body-centered-cubic single phase structure in all the compositions. Transmission Electron Microscopy (TEM) data suggest that the annealed FeCo nanoparticles are of 50–90 nm in size. The use of PEG and the annealing procedure employed ensure that the obtained nanoparticles are stable in air. This observation is well supported by both the analysis of Energy Dispersive Spectrometry (EDS) and the images of TEM which establish the formation of a thin passive oxide layer over the FeCo nanoparticles thereby resulting in the stability of the nanoparticles. The physical Property Measurement System (PPMS) reveals that the Fe 60 Co 40 composition among all the samples exhibit highest saturation magnetization of 230.14 emu/g at 5 K. & 2012 Elsevier B.V. All rights reserved. 1. Introduction Magnetic nanoparticles with high saturation magnetization are considered to be very important for magnetic energy, data storage, magnetic separation, drug delivery and imaging applica- tions [1–5]. Particularly, magnetic nanoparticles used in hyperthermia and targeted drug delivery require high saturations magnetizations for their easy manipulation through magnetic field assistance. Similarly, magnetic labels for biosensor applica- tions should possess high magnetic moments for efficient trans- location of the functionalized labels to the specific sites on the sensor surface [6,7]. Thus, the quest for identifying suitable materials for the said purpose points towards the most feasible body centered cubic (bcc) FeCo magnetic nanoparticles due to their high saturation magnetization (Ms ¼ 240 emu/g), high Curie temperature and permeability properties [8,9]. Several investigations were reported on FeCo nanoparticles synthesized using different techniques such as, thermal decom- position [10–13], wet chemical processes (by means of a reducing agent such as borohydride) [14,15], and chemical vapor deposi- tion [16]. Among the various wet chemical methods, the polyol process which involves reduction of a metal salt with a diol, typically ethylene glycol, or diethylene glycol, or a mixture of both [17], is believed to be one of the most appropriate methods, as it inherits the possibility to control the experimental condi- tions kinetically and to scale up the nanoparticle size easily [18]. Also, the polyol process is preferred over the others for simple reason that it does not emit toxic gases like carbon monoxide as in the case of thermal decomposition or contaminate the product as in the case of borohydride reduction [19,20]. Recently, there have been some reports on the synthesis of FeCo nanoparticles using polyol method [9,21–23]. Even though these studies provide high saturation magnetization, which reaches in some case to 221 emu/g, their particle sizes are relatively larger ( 4100 nm) after annealing implying an amount of lesser control on the growth of the particles. This may be disadvantageous for some applications such as targeted drug delivery in which the larger particles are likely to be obstructed by endothelial barriers. Hence, by optimizing the Fe/Co ratio, concentration of the hydroxyl ions and the reaction condition in a surfactant free facile one-pot modified polyol method, we herein successfully synthesized size-controlled and air stable FeCo nanoparticles with high saturation magnetization. The crystalline structure and shapes of the synthesized nanoparticles were examined by XRD, TEM, EDS and the saturation magnetization was measured using PPMS. Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/matlet Materials Letters 0167-577X/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2012.10.019 n Corresponding author. Tel.: þ82 42 8216236; fax: þ82 42 8226272. E-mail address: cgkim@cnu.ac.kr (C. Kim). Materials Letters 91 (2013) 326–329