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Short communication

Ferromagnetic behavior of copper oxide-nanowire-coveredcarbon fibre synthesized by thermal oxidation

Jun Zenga,b, Jincheng Xua,b,⁎, Sen Wanga,b, Peng Taoa,b, Wei Huaa,b

aKey Laboratory for the Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000, ChinabInstitute of Materials Science and Engineering, Lanzhou University, Lanzhou 730000, China

A R T I C L E D A T A

⁎ Corresponding author. Key Laboratory for tLanzhou 730000, China. Tel.: +86 931 8913577

E-mail address: xuhuan@lzu.edu.cn (J. Xu).

1044-5803/$ – see front matter © 2009 Elsevidoi:10.1016/j.matchar.2009.03.012

A B S T R A C T

Article history:Received 24 February 2009Received in revised form11 March 2009Accepted 19 March 2009

Copper oxide nanowires were synthesized on carbon fibre surfaces by annealing of copperthin films at 400 °C for 4 h in air. The nanowires were characterized with field emissionscanning electron microscope (FESEM), transmission electron microscope (TEM) and X-raydiffraction (XRD). The magnetic properties of CuO nanowires were measured with avibrating sample magnetometer (VSM). Its diameters range covered 40–100 nm and lengthsrange covered 1–3 μm. It is interesting that the CuO nanowires on the carbon fibres showedferromagnetism at room temperature.

© 2009 Elsevier Inc. All rights reserved.

Keywords:Copper oxide nanowiresCarbon fibersThermal oxidationFerromagnetism

Because of their fascinating properties and various applica-tions as compared to bulk or micro sized counterparts,nanostructures have received steady growing interest. Thestudy of the magnetic properties of oxide nanostructures is ofgreat interest currently [1]. Additionally, copper oxide (CuO)has been widely used in many fields such as in anodeelectrodes for batteries, gas sensors, field emission emitters,high temperature superconductors and magnetic storagemedia [2]. Many methods have been used to prepare one-dimensional CuO for these applications, including use ofprecursors, hydrothermal decomposition, self-catalyticgrowth processes, solve-thermal route and thermal annealing[3,4]. Recently, Qin et al. [5] reported the radial ZnO nanowireon 129 fibres hybrid structure for energy scavenging. In this

he Magnetism and Magn; fax: +86 931 8911100.

er Inc. All rights reserved

paper, CuO nanowires synthesized on carbon fibres wereexpected to exhibit magnetic property.

CuO-nanowire-covered carbon fibres (CNWCFs) weresynthesized by heating the copper-covered carbon fibres(Cu/CFs) in air. Cu/CFs were prepared by electroless platingand washed with distilled water followed by absolutealcohol. After dried in air, Cu/CFs were heated at 400 °C for4 h in air. The heating rate was controlled about 10 °C/ min.Then CNWs were synthesized on the carbon fibres. TheCNWs were characterized with X-ray diffraction (XRD), fieldemission scanning electron microscope (FESEM) and trans-mission electron microscope (TEM). The magnetic propertyof CNWs was measured with a vibrating sample magnet-ometer (VSM).

etic Materials of the Ministry of Education, Lanzhou University,

.

Fig. 1 – XRD pattern of CNWCFs.

1069M A T E R I A L S C H A R A C T E R I Z A T I O N 6 0 ( 2 0 0 9 ) 1 0 6 8 – 1 0 7 0

Fig. 1 shows the XRD pattern of the sample prepared byannealing Cu/CFs at 400 °C for 4 h in air. The results show thatonly CuO phases are observed after the annealing treat-ment in air. The copper thin film on carbon fibres converts intoCuO.

Fig. 2a shows the SEM photographs of Cu/CF. Fig. 2b, c andd show the SEM and TEM photographs of Cu/CF annealed at

Fig. 2 – a) low magnification; b) and c) high magnification SEM

400 °C for 4 h in air. The results show that the copper thinfilms on the carbon fibres convert into CNWs (Fig. 2). A largeamount of CNWs appear on the thin film surfaces (Fig. 2b andc). Fig. 2d shows TEM image of a single CNW. The diameterand length of the taper CNWs are about 40 nm and 1 μmrespectively.

The magnetic property measurements for carbon fibresand CNWCFs were performed by VSM. The results show thatthe CF exhibited paramagnetism before coated with copper(Fig. 3a). Fig. 3b shows the magnetic hysteretic loop for theCNWCFs with subtraction of paramagnetism at roomtemperature. Interestingly, the CNWCFs show ferromagneticproperty. Additionally, Chandrasekhar and Sahni [6] reportedthat oxygen vacancies caused the moment enhancement.Chen et al. [7] reported that the different defects were pro-bably caused by the combination of graphite and carbontube producing carbon and oxygen. In this paper, wesynthesized CNWCFs by thermal oxidation. The growth ofCNWCFs by the relaxation of accumulated energy causesthe defects, such as oxygen vacancies. When the CF is usedas starting reagents, which can produce carbon, the newdefects are probably caused by the reaction between carbonfrom carbon fibres and oxygen from the atmosphere.Therefore, we guess that the magnetic behavior of CNWsis the results of the defects such as oxygen vacancies.The mechanism of its magnetic behavior needs furtherinvestigation.

photographs of CNWCFs and d) TEM photograph of CNW.

Fig. 3 – The magnetic hysteretic loop of carbon fibres (a) andCNWCFs (b) at room temperature.

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In this paper, CNWCFs are synthesized by annealingCu/CFsat 400 °C for 4 h in air. Only CNWs are obtained. The CNWCFsshow ferromagnetic behavior at room temperature.

R E F E R E N C E S

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