Materials Science and Engineering B 158 (2009) 7–12 Contents lists available at ScienceDirect Materials Science and Engineering B journal homepage: www.elsevier.com/locate/mseb Synthesis and magnetic studies of flower-like nickel nanocones Ambily Mathew a , N. Munichandraiah b , G. Mohan Rao a,∗ a Department of Instrumentation, Indian Institute of Science, Bangalore 560012, India b Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012, India article info Article history: Received 19 June 2008 Received in revised form 18 November 2008 Accepted 22 December 2008 Keywords: Nickel nanocone Magnetic properties Morphology evolution abstract Flower-like nickel nanocone structures are synthesized by a simple chemical reduction method using hydrazine hydrate as the reducing agent. The structure, morphology and magnetic properties of as syn- thesized products are studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and SQUID magnetometer. The morphology evolu- tion is studied by varying the reaction temperature and concentration of nickel chloride keeping other conditions unchanged. © 2009 Elsevier B.V. All rights reserved. 1. Introduction In recent years controlling the morphology of nanostructures has been the subject of many studies due to the shape effect of these particles on their properties [1]. So far, various studies have been attempted to grow 2D and 3D organized structures by manipulation of individual units, which is a crucial step towards utilizing their magnetic, optical, catalytic and electronic prop- erties [2–7]. For example, flower-like cobalt nanocrystals by a complex precursor reaction route [8], noble metal dendrites via a simple mixed surfactant route [9], controlled synthesis of cop- per nanostructures under a direct current electric field treatment [10] and the synthesis of indium hollow spheres and nanotubes by a simple template-free solvothermal process [11] have been reported. Being an important ferromagnetic material, anisotropic Ni nanoparticles are expected to exhibit interesting magnetic prop- erties [12]. Hence Ni nanostructures have potential applications in magnetic sensors and memory devices [13]. Many groups have synthesized nickel with different morphologies such as nanoparti- cles, nanodots, nanowires, nanorods, nanocones and nanofibres by a variety of methods like hydrothermal reduction, electrodeposition and template-based methods [14–17]. Recently, Cauliflower-like Ni structures via chemical solution method [18], flower-like struc- tures with petals composed of Ni nanotips [19] and hexagonal Ni nanoplatelets via hydrothermal method [20] have been reported. With an exception of cauliflower like structure, the flower like Ni structures exhibit enhanced magnetic properties compared to bulk ∗ Corresponding author. Tel.: +91 80 22932349. E-mail address: gmrao@isu.iisc.ernet.in (G. Mohan Rao). nickel. So great attention has been given to grow flower like 3D structures by assembling individual units, expecting an enhance- ment in the magnetic properties. In the present paper, we report the synthesis of hierarchical flower-like Ni nanocones via a simple chemical reduction method without using any template or surfactant. The morphology of Ni nanostructures can be readily tuned by adjusting the experimental parameters. Since this method is simple and controllable, it can be used for commercial applications. 2. Experimental All chemicals used in this experiment were of analytical grade and used without further purification. In a typical procedure for the preparation of flower like nickel nanocones 2.37 g of NiCl 2 ·6H 2 O was dissolved in 25 ml of ethanol to obtain a green transparent solu- tion. Then this solution was added drop wise to 25 ml hydrazine hydrate (N 2 H 4 ·H 2 O) solution under stirring to form a purple col- ored solution. The pH of the solution was adjusted to 12 by adding 4 M NaOH and heated to 60 ◦ C. In about 10 min, the color of solu- tion started turning black indicating the formation of Ni particles. The stirring was continued till the solution became clear and all the particles were attached to the surface of the Teflon covered mag- netic bar. The particles were washed with de-ionized water three times and dried at 60 ◦ C in air for 1 h. Samples were also prepared by varying the concentration of NiCl 2 ·6H 2 O and the reaction tempera- ture, and the details of preparation conditions are given in Table 1. Samples numbered A–I correspond to different synthesis condi- tions listed in Table 1. All the experiments were repeated to ensure the reproducibility of microstructures. The phase purity of the products was characterized by X-ray diffraction (XRD, PHILIPS ANALYTICAL XPERT PRO) using Cu K 0921-5107/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2008.12.032