Superparamagnetic bimetallic iron--palladium

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Apr 1, 2008 - thick) with an integrated tip, a nominal spring constant of 0.7–. 3.8 N m. −1. , tip radius ... boundary exchange interaction. The alloy residing in the ... ferromagnetic and paramagnetic components vanish and thus the resultant ...

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Superparamagnetic bimetallic iron–palladium nanoalloy: synthesis and characterization

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IOP PUBLISHING

NANOTECHNOLOGY

Nanotechnology 19 (2008) 185608 (6pp)

doi:10.1088/0957-4484/19/18/185608

Superparamagnetic bimetallic iron–palladium nanoalloy: synthesis and characterization Rabia Nazir1 , Muhammad Mazhar1, M Javed Akhtar2 , M Raza Shah3 , Nawazish A Khan4 , M Nadeem2, Muhammad Siddique2, Mazhar Mehmood5 and N M Butt6 1

Department of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan Physics Division, PINSTECH, PO Nilore, Islamabad 44000, Pakistan 3 HEJ Research Institute of Chemistry, University of Karachi, Karachi 75270, Pakistan 4 Material Science Laboratory, Department of Physics, Quaid-i-Azam University, Islamabad 45320, Pakistan 5 National Centre for Nanotechnology, PIEAS, Islamabad 45650, Pakistan 6 Pakistan Science Foundation, Islamabad 44000, Pakistan 2

E-mail: [email protected]

Received 28 August 2007, in final form 23 January 2008 Published 1 April 2008 Online at stacks.iop.org/Nano/19/185608 Abstract Iron–palladium nanoalloy in the particle size range of 15–30 nm is synthesized by the relatively low temperature thermal decomposition of coprecipitated [Fe(Bipy)3 ]Cl2 and [Pd(Bipy)3 ]Cl2 in an inert ambient of dry argon gas. The silvery black Fe–Pd alloy nanoparticles are air-stable and have been characterized by EDX-RF, XRD, AFM, TEM, magnetometry, 57 Fe M¨ossbauer and impedance spectroscopy. This Fe–Pd nanoalloy is in single phase and contains iron sites having up to 11 nearest-neighboring atoms. It is superparamagnetic in nature with high magnetic susceptibility, low coercivity and hyperfine field.

and pyrolysis of organometallic precursors, the resulting alloys are in the fcc phase with particle sizes ranging between 6–11 nm and 5–10 nm, respectively [12]. Severe plastic deformation and cyclic code formation were used to prepare bulk magnetic nanocomposites of ordered L10 Fe–Pd phase and α -Fe following an atomic ordering and precipitation reaction [13]. Combinations of different stabilizers with oleic acid have been applied to prepare Fe28 Pd72 and Fe50 Pd50 nanoparticles, in the size range 11–16 nm, by the polyol reduction of Pd(acac)2 and thermal decomposition of Fe(CO)5 , respectively. The size control of nanoparticles is achieved by controlling the concentration and type of stabilizers and reaction conditions [14, 15]. Nanopowdered alloys of Pd100−x Fe x , where x = 5.4, 6, 8 and 12, of 5 nm radius have been prepared by ultrasound-assisted electrochemistry [16]. Recently, synthesis of the ordered alloy nanoparticles, based on chemical techniques, has been actively developed [17]. Fe–Pd alloy films are considered to be highly promising shape memory alloys [18] in addition to their remarkable role as hydrogen storage materials [19]

1. Introduction Bimetallic nanoparticles are of great significance because of the modification of properties observed, compared with monometallics, not only due to size effects, but also as a result of the combination of different metals, either as an alloy [1] or as a core–shell structure [2, 3]. Catalytic [4], electronic [5], magnetic [6] and optical properties [2] of the bimetallic nanoparticles have been tailored compared with monometallics. Increased mechanical strength, enhanced diffusivity, higher specific heat and electrical resistivity have also been observed [7]. Bimetallic nanoparticles have major technological applications in information storage [8] and catalysis [9] which place them on the frontiers of advanced materials chemistry. For this purpose, various synthetic routes have been approached to obtain bimetallic nanoparticles [10, 11], each of them yielding products with different physicochemical and structural characteristics. Nanopowders of the Pd-rich Fe–Pd alloys have been synthesized by ultrasound-assisted electrochemical methods 0957-4484/08/185608+06$30.00

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© 2008 IOP Publishing Ltd Printed in the UK

Nanotechnology 19 (2008) 185608

R Nazir et al

and catalysts [20, 21]. Nanoscale bimetallic particles of Fe–Pd have also been used for the treatment of chlorinated organic pollutants [22]. Controlling the structure and chemical ordering of bimetallic nanoalloys can be the starting point to prepare the building blocks for specifically tailored cluster-assembled materials [23]. Synthesis of nanoparticles, characterized by a narrow size distribution, is a new challenge in solid-state chemistry [24]. As reported in the literature [4, 25] the particle size and the properties of nanoparticles depend strongly on the specific method of preparation and the applied experimental conditions. Hence, there is a need to design a simple and economical synthetic route that enables narrow size distribution. The main purpose of this work is thus twofold: the first is to develop a simple chemical method for the synthesis of an iron–palladium nanoalloy and secondly to glean information about the different electrical and magnetic properties of the iron–palladium system at nanoscale for various technological applications.

(DMSO, ppm): 9.09–9.11 (m, 6H2 , bipyH6,6 ); 8.55–8.58 (m, 6H, bipyH3,3 ); 8.32–8.37 (m, 6H, bipyH4,4 ); 7.78–7.82 (m, 6H, bipyH5,5 ). TGA: 300–449 ◦ C (52.01% residual mass). 2.1.3. Iron–palladium alloy. 3.07 g (4.6 mmol) [Fe(Bipy)3 ] Cl2 and 3.00 g (4.6 mmol) [Pd(Bipy)3 ]Cl2 were dissolved in solution of 180 ml of distilled water and 20 ml of 33% ammonia solution. The solution was slowly evaporated with constant stirring at 40 ◦ C to get the homogeneous powder of both complexes. This powder was then taken into a Utube containing an argon inlet and outlet and was heated in a cube furnace under argon atmosphere. The temperature of the furnace was raised to 500 ◦ C at a heating rate of 0.5 ◦ C min−1 and the contents were kept at 500 ◦ C for another 24 h, then allowed to cool to room temperature under an inert atmosphere of argon gas to yield Fe–Pd (1:1) alloy. Yield 85%. 2.2. Characterization The as-synthesized Fe–Pd nanoalloy was characterized by EDX-RF using a Horiba XRF Analyzer Mensa Bio100, Japan. The XRD data of Fe–Pd was collected, by a Bruker D8 discover, Germany, at room temperature by step scanning over the angular range of 20◦  2θ  90◦ at a step size of 0.05◦ and counting time of 6 s/step. The sizes and shapes of nanoparticles were analyzed using transmission electron microscopy (TEM) (JEOL 2010), operating at 200 kV and atomic force microscopy (AFM), (Multimode, Nanoscope IIIa, Veeco, CA) in tapping mode which confirmed the alloy to be in the nanorange. The samples were prepared by spin-coating of the dispersion of the alloys in ethanol on a freshly cleaved sheet of mica substrate. AFM images were acquired with samples imaged at room temperature and repeated several times with different concentrations of samples. Silicon cantilevers (Nanoworld, Switzerland; 240 μm long, 30 μm wide, 2.8 μm thick) with an integrated tip, a nominal spring constant of 0.7– 3.8 N m−1 , tip radius