World Journal of Engineering
PREPARATION AND MAGNETIZATION OF IRON NANOWIRE ARRAYS WITH
DIFFERENT CONFIGURATIONS
C. Ke1, C. H. Cheng1,2, G..X. Yang1, and Y. Zhao1,2*
1Key
Laboratory of Advanced Technology of Materials (Ministry of Education), Superconductivity and New Energy R&D Center,
Southwest Jiaotong University, Chengdu 610031, China
2School of Materials Science and Engineering, University of New South Wales, Sydney, 2052, NSW, Australia
* Corresponding Author: yzhao@swjtu.edu.an
surface oxidation. A mirror surface was achieved by
electropolishing in a 1:5 solutions of H2ClO4 and alcohol
ethylic at 0◦C for 15 min. Two-step anodizing method was used
to make an ordered porous aluminum oxide layer on the surface
of pure aluminum [8]. Different electrolytes was used to
control the D/d ratios of the AAO templates. INAs were made
by electrodepositing iron into the pores of AAO templates with
AC electrolysis in an electrolyte containing FeSO4·7H2O
(0.5mol l-1 ), boric acid (6 g l−1) at 20◦C, 200 Hz, 15 V AC and
for 2 min. Four types of samples were obtained which have a
wire diameter d≈ 40nm and D/d ratios of 1.9, 2.2, 3.0, and 4.9,
respectively.
A X’Pert MRD diffractometer with Cu K radiation was used
characterize structure. The microstructure was analyzed by
using an environmental scanning electron microscope (ESEM)
equipped with EDS. M–H curve was measured by using
Quantum-Design SQUID XL (7 T).
Introduction
Highly ordered nano magnetic elements are of great interest in
both fundamental research and potential applications [1-3].
Compared with bulk materials, iron nanowire arrays (INAs)
exhibit many unusual properties, such as high coercivity and
perpendicular magnetic anisotropy [4,5]. Many researches have
been performed on the properties of individual nanowires,
including the dimension effect of the nanowires, magnetization
reversal mechanism. However, the magnetostatic interaction
among nanowires is not emphasized in these researches
although magnetostatic interaction can play an important role
in these nanowire arrays. Therefore, it is important to study the
macroscopic magnetic properties of nanowire arrays with
different geometric configurations since arrays’ geometric
configuration will affect the magnetostatic interaction.
Theoretical simulations have shown that besides the unique
nature of individual nanowires, interwire interaction is also an
important factor affecting macroscopic properties of the
magnetic nanowire arrays [2,3]. In order to test the theoretical
results and also provide more experimental information for
understanding the mechanism beneath the macroscopic
magnetic properties of the nanowire arrays, it is necessary to
produce relevant nanowire arrays with different configurations.
In this work, a series of INAs of different wire dimensions and
wire spacing distances have prepared through a well-controlled
electrodeposition on the ordered porous anodic aluminum oxide
(AAO) template. Their magnetic properties are also studied.
Experimental
The most important step for this study is to make ordered
porous anodic aluminum oxide (AAO) template with desired
configurations. As it is well known that the pore diameter d,
spacing D, and depth L can be controlled by anodizing voltage,
acid type and anodizing time [6]. The pore spacing D is
independent of the electrolyte and pH, and is about 2.8 nm V-1,
where V is the applied voltage [7]; and the pore diameter d can
be controlled with acid type, concentration, and preparation
temperature with the ratios D/d are roughly 1.74 to 2.15 for
H3PO4, 3.33 for H2CrO4, 4.88 for H2SO4, and 3.01 for H2C2O4
[7]. In the fabrication, pure aluminum 99.999% plate with
thickness of 0.1 mm was cut into 1 cm×3 cm pieces. These
specimens were degreased with acetone for 5 min and annealed
in 500◦C for 5 h in the inert argon atmosphere to prevent
Fig.1 SEM micrographs for well ordered AAO template. (a)
Ordered hexagonal cells with d=40nm and D=76nm,
inset shows schematic diagram of INA in AAO template
with a spacing D and a diameter d; (b) A cross-section
view of the AAO film with average pore length 11.8 m.
Results and Discussion
Fig.1(a) shows the typical results of AAO templates used for
making the INAs used for this study, averagely, d=40nm, and
1409
World Journal of Engineering
D/d=1.9. The pore density is as high as 1.3 × 1010 cm−2. It is
evident that the pores are well ordered, which provides a good
base for making highly ordered INAs. Fig. 2(b) depicts a
cross-section view of the AAO template with pores parallel to
each other and perpendicular to the surface of the AAO porous
film. The average length of the AAO nanopore is 11.8m. Fig.
2(a) shows the XRD pattern for the typical INA, indicating that
the Fe nanowire arrays are stabilized in body-centered cubic
structure with a preferential (110) texturing. Fig.2(b) shows the
SEM micrograph for the INA with the AAO template being
etched in 0.1M NaOH for 1h, inset shows the surface
morphology of the INA with AAO template after the surface
being etched for a few min. in 0.5M NaOH.. The
microstructure of the Fe nanowires illustrates clearly that the
nanowires align to each other and have uniform diameter of
about 40 nm corresponding with the pores size of the AAO
template shown in Fig.1.
around 40nm is about 2600 Oe. Our results suggest that the
INAs should have a similar magnetization behavior of to a Fe
single nanowire when its D/d is larger 3.
0.0008
M(emu)
0.0004
From inner:
D/d=1.9
2.2
3.0
4.9
0
H// wire
-0.0004
T =300K
-0.0008
-10000
-6000
-2000
2000
6000
10000
H (Oe)
Fig.3
Hysteresis loops for INAs with various D/d ratios.
3000
1000
H cw
900
H c (Oe)
Intensity (a.u.)
2500
110
(a)
800
700
600
500
2000
400
H// wire
1500
300
T =300K
200
1000
1.0
100
0
20
40
2 q (deg.)
60
80
2.0
3.0
4.0
5.0
D/d
Fig.4
Coercivity changing with D/d ratio of INAs.
Conclusion
Iron nanowire arrays (INAs) with different geometric
configurations have been prepared through electrodeposition on
the highly ordered porous anodic aluminum oxide templates.
The spacing/diameter ratios of the INAs were well controlled
by managing preparation conditions including the electrolytes
and deposition voltages. It is observed that the coercivity of the
INAs increases with the spacing/diameter ratio, and gets
saturation gradually.
Fig.2(a) XRD patterns of the Fe nanowire arrays with d=40nm
and D/d=1.9. (b) SEM micrograph for the Fe
nanowires after the AAO template has been removed
by etching in 0.1M NaOH for 1h, inset shows the
surface of the INA with AAO template after the
surface being etched for a few min. in 0.5M NaOH.
Acknowledgements The authors are grateful for the financial
support of the National Natural Science Foundation of China
under Grant No 50872116, the PCSIRT of the Ministry of
Education of China (IRT0751), the Specialized Research Fund
for the Doctoral Program of Higher Education (200806130023),
and the Fundamental Research Funds for the Central
Universities (SWJTU09ZT24).
The magnetic hysteresis loops of the INAs the AAO template
film with the field parallel to the wires at room temperature is
shown in Fig.3. It is evident that due to the single-domain
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large coercivity with Hc over 2500 Oe, which significantly
larger than 1674 Oe for the INA of d=50nm [10], but smaller
that 3250 Oe for the INA of d=16nm [5]. More interestingly,
the Hc value increases with increasing D/d ratio, and tends to
saturate gradually (see Fig.4), which is consistent to the
theoretical results [3]. It can be extrapolated from our results
that the coercivity Hcw for a single Fe nanowire of a diameter
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