High-purity nanocables of iron-containing amorphous-silica-sheathed silicon carbide were synthesized by a thermal reaction method using silicon wafer as the silicon source and growth substrate, and ferrocene as the carbon and iron catalyst precursor. The nanocables were tens of m in length and 40-60 nm in diameter. Iron oxide nanoparticles with a mean diameter of 5 nm were dispersed evenly in the amorphous silica layer. The nanocables were found to be ferromagnetic at both 10 K and room

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... ure, which indicates that they may have important potential applications in electromagnetic nanodevices. One-dimensional ͑1D͒ nanostructured materials attract extensive research interest due to their novel physical and chemical properties, and prospective applications. Among them, so-called nanocables-that contain metallic or semiconducting cores and coaxial insulating shells-have recently been studied intensively. 1-25 These unique core-shell structures provide additional opportunities for enhancing the functionality of 1D nanostructures, and may find applications in nanoscale heterostructured electronic devices. On the other hand, nanostructured magnetic materials are considered to be promising building blocks of information storage and spintronic devices. 26 It is therefore foreseeable that magnetic nanocables may have potential applications in various multifunctional electromagnetic nanodevices. Very recently, Crowley et al. 27 reported the magnetic properties of a coaxial heterostructure of germanium nanowire surrounded by cobalt nanotube sheath. However, to the best of our knowledge, there has been no report on magnetic nanocables that contain a conductive core and an insulating sheath layer so far. In this study, we report on the synthesis and magnetic properties of nanocables composed of silicon carbide core and iron oxide-implanted amorphous-silica sheath. The synthesis was performed in a quartz tube reactor inserted into a horizontal tubular furnace. A ͑100͒ one-side polished silicon wafer with an approximate size of 10 mm ϫ 15 mm was ultrasonically cleaned in ethanol and then in deionized water. The cleaned silicon wafer was put onto a graphite plate and placed in the constant temperature region of the tubular furnace. A Fe 2 O 3 powder was loaded in a ceramic boat, which was put upstream in the reactor. A ferrocene tablet with a diameter of 10 mm, cold pressed from a powder, was located near the edge of the tubular furnace ͑upstream of the Fe 2 O 3 and Si wafer͒. High-purity ͑99.999%͒ hydrogen gas was used as a carrier gas at a con-stant flux of 70 ml/ min. The furnace temperature was increased to 1150°C at a rate of 20°C / min and kept for 30 min, then the power source was switched off and the furnace cooled down to the room temperature. A uniform layer of gray-white fluffy substance with a thickness of 1 -2 mm was formed on the surface of the silicon wafer. The asprepared samples were characterized using a field emission scanning electron microscope ͑SEM͒ and a high-resolution transmission electron microcope ͑HRTEM͒ equipped with a ⍀-type energy filter and an x-ray energy dispersive spectrometer ͑EDS͒. The magnetic properties of the nanocables were studied by using a superconducting quantum interference device magnetometer. During the magnetization measurements, the nanocables were packed in a capsule randomly. Figure 1 displays the typical SEM image of an assynthesized product on a silicon wafer. Numerous entangled nanowires can be seen. The nanowires are of high purity; no catalyst particles and attached impurities can be observed. The nanowires have a mean diameter of ϳ50 nm and lengths a͒ Also at: FIG. 1. SEM image of a product found on the silicon wafer, revealing clean entangled nanowires with a mean diameter of ϳ50 nm. APPLIED PHYSICS LETTERS 88, 043105 ͑2006͒