Enhanced electromagnetic wave absorption properties of Fe nanowires in gigaherz range

Article abstract of DOI:10.1063/1.2775804

Fe nanowires with 70-200 nm in diameter and 20-50 μm in length were synthesized by a chemical vapor deposition method for electromagnetic wave absorption application. The frequency dependences of relative permittivity (εr) and permeability (μr) were strongly dependent on the diameter of Fe wires. Compared with micrometer wires or flakelike samples, nanowires exhibited a magnetic resonance (μr″) peak in the range of 1-18 GHz, suggesting that nanowires have significant effect for reducing the eddy current loss, therefore, the resin compacts of 29 vol % Fe nanowires with thicknesses of 1.3-4.0 mm provided good electromagnetic wave absorption performances in the range of 5.6-18 GHz.

Full text of DOI:10.1063/1.2775804

Enhanced electromagnetic wave absorption properties of Fe nanowires in gigaherz
range
Jiu-rong Liu, Masahiro Itoh, Masao Terada, Takashi Horikawa, and Ken-ichi Machida
Citation: Applied Physics Letters 91, 093101 (2007); doi: 10.1063/1.2775804
View online: http://dx.doi.org/10.1063/1.2775804
View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/91/9?ver=pdfcov
Published by the AIP Publishing
Articles you may be interested in
Electromagnetic and microwave absorption properties of magnetic stainless steel powder in 2–18 GHz
J. Appl. Phys. 111, 07A338 (2012); 10.1063/1.3693764
Electromagnetic characteristics of surface modified iron nanowires at x-band frequencies
J. Appl. Phys. 111, 07B545 (2012); 10.1063/1.3687139
Electromagnetic characteristic and microwave absorption properties of carbon nanotubes/epoxy composites in
the frequency range from 2 to 6 GHz
J. Appl. Phys. 105, 054314 (2009); 10.1063/1.3086630
Ag nanoshell-induced dual-frequency electromagnetic wave absorption of Ni nanoparticles
Appl. Phys. Lett. 90, 193102 (2007); 10.1063/1.2731706
Microwave absorption properties of the ZnO nanowire-polyester composites
Appl. Phys. Lett. 84, 3367 (2004); 10.1063/1.1702134
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 78.56.231.74
On: Thu, 08 May 2014 18:12:53

APPLIED PHYSICS LETTERS 91, 093101 ͑2007͒
Enhanced electromagnetic wave absorption properties of Fe nanowires
in gigaherz range
Jiu-rong Liu, Masahiro Itoh, Masao Terada, Takashi Horikawa, and Ken-ichi Machidaa͒
Center for Advanced Science and Innovation, Osaka University, 2-1 Yamadaoka, Suita,
Osaka 565-0871, Japan
͑Received 26 May 2007; accepted 2 August 2007; published online 28 August 2007͒
Fe nanowires with 70–200 nm in diameter and 20–50 ␮m in length were synthesized by a chemical
vapor deposition method for electromagnetic wave absorption application. The frequency
dependences of relative permittivity ͑␧ ͒ and permeability ͑␮ ͒ were strongly dependent on the
r
r
diameter of Fe wires. Compared with micrometer wires or flakelike samples, nanowires exhibited a
magnetic resonance ͑␮Љ͒ peak in the range of 1–18 GHz, suggesting that nanowires have significant
r
effect for reducing the eddy current loss, therefore, the resin compacts of 29 vol % Fe nanowires
with thicknesses of 1.3–4.0 mm provided good electromagnetic wave absorption performances in
the range of 5.6–18 GHz. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2775804͔
The rapid development of wireless communications and
high frequency circuit devices in gigahertz range calls for the
study of electromagnetic ͑EM͒ wave absorbing materials.
Among the candidates for EM wave absorbers, soft metallic
magnets are particularly interesting1–4 because they have
large saturation magnetization values and their Snoek’s limit
is at a high frequency level.5 Therefore, it is possible to make
thin absorbers from metallic magnetic materials in gigahertz
range.6 However, metallic magnetic materials have high
electric conductivity, which makes the high frequency per-
meability decreased drastically due to the eddy current loss
induced by EM waves.7 Metallic magnetic powders with
submicrometer particle size dispersed in nonconductive ma-
trix, such as resin or rubber, are favorable to EM wave ab-
sorbing materials. Fine metallic magnetic powders ͑e.g., Fe–
Si–Al alloy, carbonyl iron, Fe, Co, or Ni and their
permalloys͒ have been widely studied as effective EM wave
absorption materials.3,8–11 As well known, it is difficult to
prepare submicrometer powders by simply mechanical
grinding ͑MG͒ metallic magnets because the fracturing and
cold welding of powders are repeated during the MG
process.12,13 Therefore, nanocomposites such as Fe/SiO2,
Fe/ZnO, and ␣-Fe/SmO have been attracting great
interests.4,14,15 More recently, the effective EM wave absorp-
tion properties of Fe catalyst encapsulated within carbon
nanotubes to form nanowires or nanoparticles have been
reported.16,17 The encapsulated Fe nanowires showed high
anisotropy field, which resulted in magnetic resonance shift-
ing to higher frequency, suggesting that it can be used as EM
absorber in the high frequency range. However, the perme-
ability values decreased due to the addition of nonmagnetic
components into these nanocomposites. In this letter, we re-
port the absorption properties of Fe nanowires synthesized
by a chemical vapor deposition ͑CVD͒ without using tem-
plate considering easy mass production.
rate of Ar carrier gas was maintained to 150 SCCM to give
Fe microwires. When the flow rate of Ar carrier gas was
declined to 50 SCCM and the furnace temperature was kept
at 523 K, Fe flakelike samples were obtained. The as-
obtained samples were characterized by x-ray diffraction
͑XRD͒ and field emission scanning electron microscopy ͑FE-
SEM, JEOL JSM-6320 F͒. Epoxy resin composites were pre-
pared by homogeneously mixing epoxy resin with Fe wires
or flakelike samples and pressing into cylindrical-shaped
compacts. These compacts were cured at 453 K for 30 min,
and then cut into toroidal shaped samples ͑␾out: 7.00 mm,
␾in: 3.04 mm͒. In the 0.05–20.05 GHz range, the relative
permeability ͑␮ ͒ and permittivity ͑␧ ͒ values were measured
r
r
on the toroidal shaped samples using a network analyzer
͑Agilent Technologies E8363A͒. The reflection loss ͑RL͒
curves were calculated from ␮r and ␧r at the given frequency
and absorber thickness.18
Large-scale nanowires with 70–200 nm in diameter and
20–50 ␮m in length were prepared when the temperature of
reaction chamber was retained to 523 K under Ar flow rate
of 150 SCCM ͓Figs. 1͑a͒ and 1͑b͔͒. The diameter of wires
enlarged with increasing the growth temperature. When tem-
perature was increased to 673 and 823 K, the wires had di-
ameters of 8–12 ␮m ͓Fig. 1͑c͔͒ and 15–20 ␮m, respec-
Fe nanowires were prepared by thermally decomposing
Fe͑CO͒ vapor at 523 K under a flow of Ar carrier gas at a
5
rate of 150 SCCM ͑SCCM denotes cubic centimeter per
minute at STP͒ in a CVD furnace. Alternatively, the furnace
temperature was increased to above 673 K while the flow
FIG. 1. FE-SEM images of ͓͑a͒ and ͑b͔͒ as-synthesized Fe nanowires, ͑c͒
microwires synthesized at 673 K under a flow of Ar carrier gas at a rate of
150 SCCM, and ͑d͒ XRD patterns of nanowires and microwires.
a͒
Electronic mail: machida@casi.osaka-u.ac.jp
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 78.56.231.74
0003-6951/2007/91͑9͒/093101/3/$23.00 91, 093101-1 © 2007 American Institute of Physics
On: Thu, 08 May 2014 18:12:53

093101-2
Liu et al.
Appl. Phys. Lett. 91, 093101 ͑2007͒
FIG. 3. Frequency dependences of ͑a͒ ␮Ј and ͑d͒ ␮Љ for the resin compos-
FIG. 2. Frequency dependences of ͑a͒ ␧Ј and ͑b͒ ␧Љ for the resin composites
r
r
r
r
ites with 29 vol % Fe nanowires, microwires ͑8–12 ␮m in diameter͒, and
with 29 vol % Fe nanowires, microwires ͑8–12 ␮m in diameter͒, and flake-
flakelike samples in the 0.05–18 GHz range.
like samples in the 0.05–18 GHz range.
tively. On the other hand, we found that the morphology of
Fe was strongly dependent on the flow rate of Ar gas, which
frequency range ͓Fig. 3͑b͔͒. The ␮Љ curve exhibited a peak in
r
a broad frequency range ͑1–18 GHz͒. In comparison with Fe
nanoparticles,15 the magnetic resonance of Fe nanowires
shifted to higher frequency, probably due to the large shape
anisotropy field of nanowires. When the volume fraction of
was related to the carrying quantity of Fe͑CO͒ into the re-
5
action chamber. Decreasing the flow rate of Ar gas, the flake-
like samples of Fe began to form. When the flow rate was
decreased to 50 SCCM at 523 K, the final product mainly
contained the irregular shaped flakelike samples with edge
lengths of above 100 ␮m and thicknesses of 6–30 ␮m, ac-
companying with a small fraction ͑less than 1%͒ of nano-
wires. XRD data confirmed that the wires ͓Fig. 1͑d͔͒ and
flakelike samples are ␣-Fe.19
nanowires in the composites increased to 30 vol %, the ␧Ј
r
and ␧Љ values increased markedly to 15 and 0.9, respectively,
r
which indicates lower electric resistivity, finally resulting in
the decrease of ␮Ј and ␮Љ. For the resin composites with
r
29 vol % Fe microwires ͑r8–12 ␮m in diameter͒, the ␮Ј
r
value decreased from 5.1 to 0.7 in the 0.05–18 GHz range.
Figure 2 show that the real part ͑␧Ј͒ and the imaginary
r
Furthermore, the ␮Љ value also declined from 1.6 to 0.3 with
r
part ͑␧Љ͒ of relative permittivity for the resin composites with
frequency, and no magnetic resonance peak was present in
the 0.05–18 GHz range. When the resin composites con-
tained 29 vol % Fe flakelike samples, the ␮Ј and ␮Љ values
r
29 vol % Fe nanowires were almost constant between 0.5
and 18 GHz, for which the relative permittivity ͑␧r=␧Ј
r
r
r
− j␧Љ͒ showed less variation ͑␧Ј= ϳ10 and ␧Љ= ϳ0.5͒. How-
decreased sharply from 3.4 and 1.25 to 0.4 and 0.1 in the
0.05–18 GHz range, respectively. The above results indi-
cated that the dispersive behavior of permeability was deter-
mined mainly by the size rather than the morphology of Fe.
Figure 4͑c͒ shows the typical relationship between RL
and frequency for the resin composites with 29 vol % Fe
nanowires. The RL values of less than −20 dB were obtained
in the 5.6–18 GHz ͑G and X bands range͒ with absorber
thicknesses of 1.3–4.0 mm, and a minimum RL value of
−47 dB was observed at 9.4 GHz with a thickness of
2.0 mm. Compared with the resin composites of ferrites used
as conventional EM wave absorption materials, the
thicknesses of Fe nanowire absorbers decreased by about
30%–50% in the same high gigahertz region.21,22 However,
for the resin composites with 29 vol % Fe microwires
͑8–12 ␮m in diameter͒ or flakelike samples, they only gave
weak absorption ͓Figs. 4͑a͒ and 4͑b͔͒. It is well known that
the relative permittivity ͑␧Ј− j␧Љ͒ and permeability ͑␮Ј
r
r
r
ever, for the resin composites with 29 vol % Fe microwires
͑8–12 ␮m in diameter͒, the ␧Ј and ␧Љ values declined with
r
increasing frequency from 35 and 2r6 to 16 and 3 in the
0.05–18 GHz, respectively. The similar dispersive behavior
was also observed for the ␧Ј and ␧Љ curves of the resin com-
r
r
posites with 29 vol % Fe flakelike samples in the
0.05–18 GHz, in which the ␧Ј and ␧Љ values decreased from
44 and 76 to 20 and 5.5, resrpectiverly. Comparing with the
resin composites of microwires and flakelike samples, nano-
wire composites exhibited a lower permittivity level, which
can be attributed to the decrease of space-charge polarization
between Fe nanowires isolated by epoxy resin more effi-
ciently after mixing with epoxy resin homogeneously. This
result also agrees with the previous work, in which the per-
mittivity of rubber composites containing Fe particles de-
creased with decrease in Fe particle size.20 The real part of
relative permeability ͑␮Ј͒ gradually declined from 4.5 to
r
r
r
r
0.98 with increasing frequency in the 0.05–18 GHz range
for the resin composites of Fe nanowires, as shown in
Fig. 3͑a͒. The imaginary part of the relative permeability
− j␮Љ͒ of materials determine the EM wave absorbing char-
r
acteristics, such as frequency, thickness, and absorbing band-
width. In this work, the measured permittivity values are of
the same order of magnitude, and no dielectric response peak
͑␮Љ͒ increased from 0.05 to 0.96 over a range of
r
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 78.56.231.74
0.05–5.6 GHz, and then decreased gradually in the higher
was observed in the 0.05–18 GHz range ͑Fig. 2͒. Therefore,
On: Thu, 08 May 2014 18:12:53

093101-3
Liu et al.
Appl. Phys. Lett. 91, 093101 ͑2007͒
in the weak internal interaction of Fe nanowires, which
might be another key factor for the spectra of ␮Ј and ␮Љ.
r
r
In summary, large-scale Fe nanowires were prepared by
a CVD method without using template. The resin composites
with Fe nanowires showed good EM wave absorbing char-
acteristics in the 5.6–18 GHz ͑G and X bands range͒. This
study demonstrated the possible application of producing
thin and light EM wave absorbers from Fe nanowires. By
comparing nanowires with micrometer wires or flakelike
samples, the different absorption properties mainly resulted
from the size effect of Fe on the frequency dependences of
relative permittivity and permeability on their resin
composites.
This work was supported by Grant-in-Aid for Scientific
Research No. 15205025 from the Ministry of Education, Sci-
ence, Sports, and Culture of Japan, and Industrial Technol-
ogy Research Grant Program in 2003 from New Energy and
Industrial Technology Development Organization ͑NEDO͒
of Japan.
1Y. Naito and K. Suetaki, IEEE Trans. Microwave Theory Tech. 19, 65
͑1971͒.
2J. L. Wallace, IEEE Trans. Magn. 29, 4209 ͑1993͒.
3P. Toneguzzo, G. Viau, O. Acher, F. Fievet-Vincent, and F. Fievet,
Adv. Mater. ͑Weinheim, Ger.͒ 10, 1032 ͑1998͒.
4A. Butera, J. N. Zhou, and J. A. Barnard, J. Appl. Phys. 87, 5627 ͑2000͒.
5J. L. Snoek, Physica ͑Amsterdam͒ 14, 207 ͑1948͒.
6S. Yoshida, M. Sato, E. Sugawara, and Y. Shimada, J. Appl. Phys. 85,
4636 ͑1999͒.
7D. Rousselle, A. Berthault, O. Acher, J. P. Bouchaud, and P. G. Zerah,
J. Appl. Phys. 74, 475 ͑1993͒.
8M. Sato, S. Yoshida, E. Sugawara, and Y. Shimada, J. Magn. Soc. Jpn. 20,
4214 ͑1996͒.
FIG. 4. Frequency dependences of the reflection loss ͑RL͒ for the resin
composites of 29 vol % Fe: ͑a͒ flakelike samples, ͑b͒ microwires ͑8–12 ␮m
in diameter͒, and ͑c͒ nanowires at different thicknesses in the 0.05–18 GHz
range.
9M. Matsumoto and Y. Miyata, IEEE Trans. Magn. 33, 523 ͑1997͒.
10L. Olmedo, G. Chateau, C. Deleuze, and J. L. Forveille, J. Appl. Phys. 73,
6992 ͑1993͒.
11G. Viau, F. Ravel, O. Acher, F. Fievet-Vincent, and F. Fievet, J. Appl.
Phys. 76, 6570 ͑1994͒.
12L. W. Deng, J. J. Jiang, S. C. Fan, Z. K. Feng, W. Y. Xie, X. C. Zhang, and
H. H. He, J. Magn. Magn. Mater. 264, 50 ͑2003͒.
the EM wave absorbing characteristics strongly depend on
the magnetic resonance of these composites. From the fre-
quency dependence of relative permeability for the resin
composites with Fe microwires ͑8–12 ␮m in diameter͒ or
flakelike samples ͑Fig. 3͒, one can observe that the ␮Ј and
13N. T. Rochman, K. Kawamoto, H. Sueyoshi, Y. Nakamura, and T. Nishida,
J. Mater. Process. Technol. 89, 367 ͑1999͒.
14M. Pardavi-Horvath and L. J. Swartzendruber, IEEE Trans. Magn. 35,
3502 ͑1999͒.
␮Љ values drastically decline with frequency, and no rmag-
15S. Sugimoto, T. Maeda, D. Book, T. Kagotani, K. Inomata, M. Homma,
H. Ota, Y. Houjou, and R. Sato, J. Alloys Compd. 330, 301 ͑2002͒.
16R. Che, L. Peng, X. Duan, Q. Chen, and X. Liang, Adv. Mater.
͑Weinheim, Ger.͒ 16, 401 ͑2004͒.
r
netic resonance peak is present in the 0.05–18 GHz range.
However, the ␮Ј value gradually decreases with increasing
r
frequency and one magnetic resonance peak can be observed
in the 1.0–18 GHz range for the resin composites with Fe
nanowires. The above experimental results suggested that the
Fe wires with nanoscale diameter have significant effect for
reducing the eddy current loss and possess a remarkable fea-
ture for EM wave absorption in the 1.0–18 GHz range. On
the other hand, the Fe nanowires are isolated by the coating
of epoxy resin, therefore, such composite morphology results
17H. M. Kim, C. Y. Lee, J. Joo, S. J. Cho, H. S. Yoon, D. A. Pejakovic, J. W.
Yoo, and A. J. Epstein, Appl. Phys. Lett. 26, 589 ͑2004͒.
18H. M. Musal, Jr. and H. T. Hahn, IEEE Trans. Magn. 25, 3851 ͑1989͒.
19H. E. Swanson, R. K. Fuyat, and G. M. Ugrinic, JCPDS, International
Center for Diffraction Data, Card No. 6-0696 ͑1955͒.
20S. Kim, S. Kim, Y. Yoon, and K. Lee, J. Appl. Phys. 97, 10F905 ͑2005͒.
21H. J. Kwon, J. Y. Shin, and J. H. Oh, J. Appl. Phys. 75, 6109 ͑1994͒.
22P. Singh, V. K. Babbar, A. Razdan, R. K. Puri, and T. C. Goel, J. Appl.
Phys. 87, 4362 ͑2000͒.
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 78.56.231.74
On: Thu, 08 May 2014 18:12:53