Letter Synthesis and magnetic properties of core-shell Fe 70 Co 30 @Ag dendritic nanostructures B. Bhoi a,b , Vidyadhar Singh a,c,⇑ a Department of Physics and Meteorology, Indian Institute of Technology Kharagpur, Kharagpur 721302, India b Centre for Research in Nanotechnology and Science (CRNTS), Indian Institute of Technology, Bombay 400076, India c Department of Physics, Lovely Professional University, Punjab 144402, India article info Article history: Received 14 October 2011 Received in revised form 29 June 2012 Accepted 2 July 2012 Available online 11 July 2012 Keywords: Nanostructured materials Chemical synthesis Mechanical alloying Magnetization TEM abstract Core–shell Fe 70 Co 30 @Ag dendritic nanostructures were successfully synthesized via a simple transmetal- lic redox method at room temperature, employing a mixed Fe 70 Co 30 nanoparticles, and AgNO 3 solution. The Fe 70 Co 30 @Ag nanostructures demonstrate a leaf like structure with different lengths (100–300 nm) and widths (50 nm) connected to the main branch which is of several tens of lm long. The Ag coating of thickness 8 nm on Fe 70 Co 30 enhances the plasmonic and antioxidation properties of Fe 70 Co 30 @Ag core–shell nanostructure. The saturation magnetization (M S 62 emu/g) and coercivity (H C 144 Oe) at room temperature clearly suggest that the Fe 70 Co 30 @Ag nanostructures is protected from the oxidation due to the Ag coating. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction The synthesis of core–shell type magnetic nanostructure such as nanospheres, nanocubes, nanotubes, etc. with a magnetic cores and a non-magnetic shell (Al 2 O 3 , C, Ag, Au, etc.) have been the sub- ject of substantial research in recent years because of their wide- spread potential applications in catalysis, drug delivery, magnetic sensors, photonic crystals, etc. [1–6]. Although Fe, Ni, Fe 3 O 4 , etc. nanoparticles (NPs) have frequently been chosen as magnetic cores but Fe 70 Co 30 alloy cores should be better from application point of view due to its higher saturation magnetization (MS).With regard to this background, we thought of fabricating the core–shell den- drite nanostructure with Ag as shell and with Fe 70 Co 30 alloy NPs as core to impress optical properties to the magnetic core particles [7,8]. Besides, as far as we know, the Fe 70 Co 30 @Ag core–shell den- drite nanostructure has not been reported yet. In this work, we report for the first time the synthesis of Fe 70 Co 30 @Ag core–shell dendrite nanostructure with a complete study of its morphology, structure, thermal stability, optical and magnetic properties. 2. Experimental details Fe 70 Co 30 @Ag dendrite nanostructures were synthesized using transmetallic redox method employing an ultrasonicated reaction between Fe–Co alloy NPs and AgNO 3 solution. The synthesis process consisted of two steps. In the first step Fe 70 Co 30 alloy NPs were prepared using high energy ball milling followed by the method discussed in our previous report [9]. In the second step this Fe 70 Co 30 alloy nanoparticles were ultrasonicated for 5–10 min and added to an aqueous solution of 1 M AgNO 3 . The silver coating was accomplished via an ion-exchange reaction viz Fe–Co + 5 Ag + ? 5 Ag + Fe 3+ –Co 2+ occurring at the surface of Fe–Co particles due to which the surface Fe–Co got replaced by a layer of Ag. The surface topology and in situ chemical analysis was performed by a field emis- sion scanning electron microscope (FESEM) equipped with the energy-dispersive- X-ray (EDX) spectroscopy (Carl ZEISS-SUPRA) and high resolution transmission electron microscope (HRTEM, JEOL-JEM-2100). The structure of the samples were studied by high resolution X-ray diffraction (XRD, X’pert Pro, PW 3040) under Cu Ka radiation (k = 1.54056 Å). The thermal analysis was done in air by a Perkin- Elmer thermal analyzer (Pyris Diamond TG). The optical properties were measured on a Perkin Elmer, Lambada 25, UV-Visible (UV–Vis) spectrometer. A PHI 5800 X-ray photoelectron spectrophotometer (XPS) was used to measure XPS bands from the particles under 10 8 Pa pressure, with Al Ka 1,2 radiation of 1486.60 eV energy operating at 12 kV and 20 mA as the excitation source. The magnetic properties were studied by a vibrating sample magnetometer (VSM 736, Lake Shore Cryotronics). 3. Results and discussion The FESEM and TEM images of Fe 70 Co 30 @Ag are shown in Fig. 1, which reveals the large-scale leaf like dendrite hierarchical struc- tures consisting of several leaves with different lengths (100– 300 nm) and widths (50 nm) connected to the main branch of several tens of lm. The growth of Fe 70 Co 30 @Ag dendrite nanostruc- 0925-8388/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jallcom.2012.07.002 ⇑ Corresponding author. Present address: Okinawa Institute of Science and Technology, Okinawa, Japan. Tel. +91 3222 255303. E-mail address: vidyadhar@iitkgp.ac.in (V. Singh). Journal of Alloys and Compounds 541 (2012) 468–471 Contents lists available at SciVerse ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom