Electrical conductivity and magnetic properties of core-shell silver-coated magnetite composite nanoparticles
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Electrical conductivity and magnetic properties of core-shell silver-coated magnetite composite nanoparticles prepared by electroless deposition of silver on magnetite nanopowder are found to be affected mainly by the pressure used when preparing the nanoparticles sample cylinder and the Ag content in the nanoparticles. The electrical conductivity can be enhanced by increases of both the pressure and the Ag content. Direct current volume electrical resistivity of the nanoparticles with 40 wt% silver content is close to the order of 104 X cm when the pressure is larger than 1 106 Pa. The saturation magnetization of the nanoparticles almost reduces linearly with increasing the silver content. According to the rule of mixtures, the resistivity of the nanoparticles is calculated. But it shows that the calculated values have a large deviation with the corresponding measured ones. As a comparison, resistivity and saturation magnetization of the mixtures consisting of silver and magnetite nanopowder are also measured. It will be an effective method to adjust the electromagnetic properties of the nanoparticles by changing the silver content. I. INTRODUCTION
Compared with a bulk material, nanoparticles exhibit many unique features in material properties (e.g., thermal, optical, electrical, magnetic and catalytic) due to their small-size effect, surface effect and quantum size effect. So, they have attracted great research interest over the past two decades. Magnetite (Fe3O4) exhibits the strongest magnetism of any transition metal oxide and high Curie temperature (Tc) of 858 K.1,2 But Fe3O4 is a material with half metallicity (i.e., electrical resistivity of bulk magnetite crystal is q 5 1.9 102 X cm at room temperature) and weak antioxidation capability.2–4 Silver (Ag) is the most conductive bulk metal (1.6 106 X cm electrical conductivity at room temperature) and has good chemical inertness. In addition, Ag can be facilely fabricated into nanoparticles5–7 and these nanoparticles have been widely used in the fields of biomedicine, electronics, optics and optoelectronics.8 In order to acquire the materials that possess the properties of both Ag and Fe3O4, Ag-Fe3O4 composite materials need to be prepared. Generally, metal–nonmetallic (or metal–half metallic and metal–semiconductor) composite materials can be prepared by many methods including coprecipitation,9 ball milling,10 electroless deposition11 and chemical reduction.12 Among these methods, electroless deposition, based on autocatalytic reduction of metallic salt complexes, a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.150 J. Mater. Res., Vol. 27, No. 14, Jul 28, 2012
has many advantages, the most notable of which is uniform dispersion of the metallic coating.13 For example, the electroless deposition of metals [e.g., Ag, gold (Au), copper (Cu) and nickel (Ni)] on the surface of nonmetallic (or halfmetallic and semiconductor) nanosized particles [e.g., carbon (C) nanotubes, silicon carbide (SiC) nanofibers and
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