Electrochimica Acta 54 (2009) 6543–6547
Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Structure and magnetic properties of Fe1 Co nanowires in self-assembled arrays
−x
x
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a
a
b
a
a
a,∗
G.H. Yue , X. Wang , L.S. Wang , P. Chang , R.T. Wen , Y.Z. Chen , D.L. Peng
a
Department of Materials Science & Engineering, Research Center of Materials Design & Applications, Xiamen University, Xiamen 361005, People’s Republic of China
School of Physical Science & Technology, Lanzhou University, Lanzhou 730000, People’s Republic of China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
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Fe1 Co nanowires in self-assembled arrays with varying compositions were produced by the template-
Received 22 January 2009
Received in revised form 2 June 2009
Accepted 15 June 2009
assisted pulsed electrochemical deposition method. The structural and magnetic properties of the arrays
were investigated using several experimental techniques. TEM analyses indicated that the nanowires
were regular, uniform, 8 m in length and 50 nm in diameter. The results of X-ray diffraction indicated
that the body-centered-cubic (bcc) (␣), face-centered-cubic (fcc) (␥), and hexagonal-close-packed (hcp)
Available online 23 June 2009
(
) Fe–Co phases appeared in different compositions. Magnetic measurements showed that the coercivity
Keywords:
and squareness of the hysteresis loops of the Fe1−xCox changed with their compositions, which may be
attributable to shape anisotropy. The room temperature Fe Mössbauer spectra of the arrays of the
Fe1−xCox nanowires revealed strong shape anisotropy.
Fe1−xCox nanowires
Magnetic properties
Electrochemical deposition
57
©
2009 Elsevier Ltd. All rights reserved.
1. Introduction
2. Experimental
In recent years, studies of one-dimensional (1D) nanostruc-
tures have attracted considerable attention [1–4]. Preparation of
metal nanowires and/or nanotubes is also of interest because these
nanostructures show interesting electrical [5] and magnetic [6–8]
properties. Furthermore, these structures have potential appli-
cations in future generations of nanodevices [9]. In particular,
the fabrication of ordered magnetic metal nanowire arrays has
attracted considerable scientific and commercial attention due to
their potential utilization in magnetic recording media [10,11],
sensors and other devices [12,13]. Many techniques have been
developed to produce nanoscale materials. Among them, electrode-
position of nanowires into self-assembled alumina is a simple,
low-cost, high-throughput technique [14,15]. We fabricated Fe–Co
alloy nanowire arrays using this method and studied their magnetic
properties.
Arrays of FeCo nanowires were prepared by pulsed electrodepo-
sition of Fe and Co into anodic aluminum oxide (AAO) templates.
The preparation of AAO templates has been described elsewhere in
detail [20]. In this experiment, high purity Al foils (99.999%) were
◦
annealed at 500 C for about 48 h and anodized at 40 V (dc) in 0.3 M
◦
H C O aqueous solution at 0 C for 1 h. After the porous templates
2
2
4
were removed, a second anodization step was performed under
the same conditions. A mixture of an aqueous solution containing
FeSO ·7H O (0.5 M/L), H BO (0.6 M/L), and ascorbic acid (4 mM/L)
4
2
3
4
2+
was used for the Fe aqueous solution. Similarly, a mixture of
2+
CoSO ·7H O (0.5 M/L) and H BO (0.6 M/L) was used for the Co
4
2
3
4
2+
2+
aqueous solution. The Fe :Co ion ratios in the baths were var-
ied to obtain Fe1 Cox nanowires with different compositions. The
−x
pH value of the electrolyte was maintained at about 3.0. Electrode-
position was conducted using a pulsed electrical source at 50 Hz
and 10 V (ac). The electrodeposition time was 5 min, and graphite
was used as the counterelectrode. After deposition, samples were
kept in pure alcohol solution to avoid oxidation. For convenience,
the nanowire arrays with AAO templates were removed from the
residual Al substrate using a saturated aqueous solution of HgCl2
before the X-ray diffraction (XRD) and magnetic properties were
measured. Prior to transmission electron microscopy (TEM), the
nanowires were liberated by dissolving the AAO templates in NaOH
aqueous solution.
In the past, different groups have tried to produce Fe(
1−x)
Cox
nanowires of different stoichiometries. Most synthetic methods
have been based on templates, such as mesoporous alumina [14,15]
or metal step edges [16]. However, the nanowires generated by
thesetechniquesexhibitedamorphous-likeorpolycrystallineprop-
erties [14–17]. The thermal decomposition of Fe and Co carbonyls
in the presence of strong magnetic fields resulted in the creation of
polycrystalline FeCo nanowires [18]. To circumvent these problems,
the formation of single crystalline wires [19].
Structural characterizations were performed by means of XRD
using a Rigaku D/Max-2400 diffractometer with a Cu K␣ ray. The
atomic percentages of Fe and Co in the nanowires were obtained by
atomic absorption spectroscopy (AAS). The morphology of the AAO
films and the regularity of the nanowire spacing were monitored by
∗ Corresponding author. Tel.: +86 592 2180155; fax: +86 592 2180155.
0
013-4686/$ – see front matter © 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2009.06.037