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Electromagnetic and absorption properties of nano-sized and micro-sized Fe4N particles
Accepted Manuscript Electromagnetic and absorption properties of nano-sized and micro-sized Fe4N particles Meijie Yu, Yong Xu, Qiong Mao, Fazhan Li, Chengguo Wang PII:
S0925-8388(15)31261-5
DOI:
10.1016/j.jallcom.2015.10.005
Reference:
JALCOM 35560
To appear in:
Journal of Alloys and Compounds
Received Date: 7 April 2015 Revised Date:
1 July 2015
Accepted Date: 1 October 2015
Please cite this article as: M. Yu, Y. Xu, Q. Mao, F. Li, C. Wang, Electromagnetic and absorption properties of nano-sized and micro-sized Fe4N particles, Journal of Alloys and Compounds (2015), doi: 10.1016/j.jallcom.2015.10.005. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Electromagnetic and absorption properties of nano-sized and micro-sized Fe4N particles Meijie Yu a, *, Yong Xu b, Qiong Mao a, Fazhan Li a, Chengguo Wang a, * College of Materials Science and Engineering, Shandong University, Jinan 250061, People’s
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a
Republic of China b
College of Materials Science and Engineering, Shandong Jianzhu University, Jinan 250101,
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People’s Republic of China
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ABSTRACT:
Single-phase Fe4N has been synthesized by gaseous nitriding micro-sized and nano-sized Fe particles at 793K under ammonia atmosphere. The electromagnetic properties of their wax composite with 75 wt. % magnetic particles have been investigated within the frequency range of
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1–18 GHz. Both size and phase effects on the microwave absorption properties were discussed on the results of scanning electronic microscopy, X-ray diffraction, hysteresis loop, and the frequency dependence of complex permittivity and permeability. The results show that
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nano-sized particles have superior absorbing performance at lower frequency band than the
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corresponding micro-sized ones, which is mainly attributed to the higher dielectric constant caused by interfacial polarization. The Fe4N composites exhibit much stronger absorption in 2–8 GHz than Fe composites. The reflection loss (RL) values of less than -10 dB are observed in a wide frequency bandwidth from 1.8 to 11 GHz for nano-sized Fe4N composite with absorber
*
Corresponding author at: College of Materials Science and Engineering, Shandong University, Jinan 250061, People’s Republic of China. (Meijie Yu) Tel: +86-531-88396181 E-mail address: [email protected] (Meijie Yu); [email protected] (Chengguo Wang)
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thickness of 1.2–5.0 mm. Its minimum RL value (RLmin = -33 dB) appears at 3.5 GHz with a thickness of 3.0 mm. This study demonstrates the possible application of producing thin and light
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absorbers from nano-sized Fe4N particles for microwave absorption at S and C bands (2–8 GHz). Keywords: iron nitride; nanoparticle; electromagnetic property; X-ray diffraction 1. Introduction
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Microwave electromagnetic and absorption property of magnetic nanoparticles is a topic of
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interest due to the rapid development of wireless communication, ultrafast high density data storage and the military purpose in radar absorption [1]. Compared with the commonly used ferrites, ferromagnetic metal-based nanomaterials are promised to be more suitable as microwave absorbers with thin thickness and wider working frequency owing to their larger saturation
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magnetization and higher Snoek’s limit at high frequency [2-4]. As an important ferromagnetic metal, iron (α-Fe) has been widely used as a candidate for microwave absorption applications because of low magneto-crystalline anisotropy, high Curie temperatures (Tc = 1043K), and the
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highest room-temperature saturation magnetization (Ms = 218 emu/g) of any ferromagnetic
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elements [5]. Nevertheless, the greatest weakness of iron is its reactivity, especially with respect to water and oxygen. This general weakness is greatly multiplied in the case of iron nanoparticles, where the iron rapidly and completely oxidized in air. Recently, iron nitrides have received much attention by virtue of the excellent magnetic properties, low coercivity in combination with significantly improved corrosion resistance over pure iron [6-8]. Among the ferromagnetic nitrides, γ’ phase of iron nitride (Fe4N) is of special interest. This nitride has a perovskite-type structure, in which N is located at the body center 2
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position of fcc-Fe [9]. Due to its large saturation magnetization [10], lower coercive force [11], and chemical stability [12], the Fe4N has been considered as an important material in the fields
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of ferrofluids, high density magnetic recording, and magnetic refrigeration. Considerable studies have been done theoretically and experimentally on the electronic structure and magnetic
properties of Fe4N [13, 14]. However the microwave absorption properties of nanoparticle Fe4N
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in the 2-18 GHz frequency range have seldom been reported to date. Moreover, the
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ferromagnetic particles and their composites used as microwave absorbers often possess a size of micrometer or nanometer. The relationship between the electromagnetic properties and the size effect has not been well understood.
In this paper, we demonstrate excellent microwave absorption by single-phase Fe4N
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nanoparticles over broad frequency range. For the thickness of the absorbers between 1.5 and 3mm, the reflection loss (RL) values less than -10 dB are obtained in a range of 2-8 GHz, which covers the whole S band (2-4 GHz) and C band (4-8 GHz). The size and phase effects on the
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electromagnetic and absorption properties of Fe4N and Fe particles have been analyzed in detail.
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2. Experimental procedure
The starting materials to prepare Fe4N particles were the commercial micro-sized carbonyl iron powder with 99.5 % purity and the nano-sized pure iron powder without any surface treatment. Fe4N particles were prepared by gaseous nitriding method. The iron particles of micro-size and nano-size were heat treated under the same nitriding conditions: temperature 793 K, the ammonia decomposition rate ~68 %, heat treatment time 5 h. From room temperature to 793 K, nitrogen was used to protect the materials from oxidation; up to 793 K, nitrogen was 3
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substituted by ammonia. For the aim of preventing oxidation and aggregation, the nano-sized Fe particles were coated with polyvinylpyrrolidone (PVP) in our laboratory before gaseous nitriding.
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In a typical process, 10 g Fe nanoparticles, isolated with air, were added into PVP aqueous solution (0.02 g/ml) and mechanical stirred for 20 min. The coated Fe nanoparticles were precipitated by magnet, washed with alcohol and then dried in vacuum.
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The X-ray powder diffraction data was collected in 2θ range of 10-90° using a Bruker AXS
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D8 advanced diffractometer with Cu Kα radiation under 40 kV and 50 mA. The morphology of the magnetic particles was observed by a field emission scanning electron microscopy (FESEM, SU-70). Static magnetic measurement was carried out on a vibrating sample magnetometer (VSM, JDAW-2000＆D) at room temperature with an applied field up to 10 kOe. For microwave
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absorption measurements, the samples were the wax composite with 75 wt. % magnetic particles, which were made into toroidal shape with an outer diameter of 7.00 mm and an inner diameter of 3.04 mm. The complex permeability and permittivity over 1-18 GHz were calculated from the
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S-parameters measured using a vector network analyzer (VNA, HP 8722ES) with a
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transmission-reflection-line (TRL) calibration. 3. Results and discussion
3.1 SEM and XRD analysis
Fig.1 shows the SEM morphologies of the micro-sized Fe particles before and after nitriding treatment. The diameter (1-4 µm) keeps almost unchanged, while the shape becomes slightly irregular after nitriding treatment. Meanwhile, the surface morphology of the particles changes from smooth to coarse. Compared with the micro-sized particles, more obvious changes 4
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can be observed in nano-sized ones as shown in Fig.2. After nitriding treatment, the nano-sized Fe particles lost their spherical appearance, becoming more irregular with lamellar texture.
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The XRD patterns (Fig.3) confirm that the phase compositions change from α-Fe to single-phase γ’-Fe4N for both the micro- and nano-sized particles after nitriding under the certain conditions. We found that the phase composition was strongly dependent on the ammonia
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decomposition rate. In order to obtain single-phase Fe4N, the ammonia decomposition rate must
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be confined in a much narrower range for nano-sized particles than the micro-sized ones. Mixed phases of α-Fe and γ’-Fe4N were observed for the nano-sized particles when decreasing the ammonia decomposition rate from ~68 %. This behavior is presumably a result of Gibbs-Thomson effect [15]. The grain size estimated by Scherrer’s formula is 30-40 nm and
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40-50 nm for the nano-sized and micro-sized Fe4N particles, respectively. 3.2 Electromagnetic properties analysis
Fig.4 shows the hysteresis loops of the Fe4N particles of the two different sizes, which
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exhibit that both samples have excellent soft magnetic properties. The Ms value of micro-sized
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Fe4N particles is 196 emu/g, which is a little higher than the value (188 ± 2 emu/g) reported previously [16]. The Ms value of nano-sized Fe4N particles is 221 emu/g, which is higher than not only that of micro-sized Fe4N particles in the present study, but also the reported sheet-form Fe4N (179 emu/g) [14] and pure iron (218 emu/g) [15]. Moreover, the approach of nano-sized particles to saturation occurs at a much smaller field. It means that their static permeability is higher than that of relatively larger particles. This is confirmed by the following results in Fig.5 (d). Meanwhile, the nano-sized Fe4N particles demonstrate higher coercivity (Hc, 118 Oe) than 5
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that of the micro-sized Fe4N (38 Oe). Generally, the Hc of magnetic nanoparticles is mainly composed by crystalline anisotropy and shape anisotropy [17]. Typically, due to symmetry
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reasons, the magneto-crystalline anisotropy is much weaker in cubic materials [18]. As confirmed by XRD results, both the Fe4N particles have nano-sized crystals of fcc structure, implying that the crystalline anisotropies of the Fe4N particles of different sizes are almost the
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same. Therefore, the difference in Hc can be attributed to the shape anisotropy. The nano-sized
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Fe4N particles possess much stronger shape anisotropy than the micro-sized ones thus resulting in higher Hc.
Fig.5 (a) and (b) show the frequency dependence of the relative complex permittivity ( = − ) for the wax composites with 75 wt. % Fe or Fe4N particles. For the wax composites with the micro-sized Fe particles, the real part and the imaginary part of relative
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permittivity keep almost constant ( = ~7.5 and = ~0.1) with increasing frequency from 1 to 18 GHz. The similar characteristics was also observed for the composites with nano-sized Fe
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particles. The and values slightly decline with increasing frequency from 15.7 and 4.1 to
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13.4 and 2.7 in 1-4 GHz, and keep almost constant ( = ~13 and = ~2.2) between 4 and 18 GHz. Comparing with the micro-sized Fe particles, the nano-sized Fe particles exhibited a higher permittivity level, which can be attributed to the increase of space-charge polarization between nano-sized Fe particles isolated by PVP, more efficiently after mixing with wax homogeneously. Compared with Fig.5 (a), Fig.5 (b) exhibits obvious differences in and curves. Dielectric resonance peaks were observed at 12.5 and 14.4 GHz for the composites with Fe4N particles of micro-size and nano-size, respectively; while no dielectric resonance peak was found for the 6
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composites with Fe particles. This result indicates Fe4N particles possess different polarization mode with Fe particles. From Fig.5 (b), the composite with nano-sized Fe4N particles also have a
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higher than that with micro-sized ones. Therefore, either for Fe or Fe4N, the higher dielectric constant of nano-sized particles than micro-sized ones mainly due to the interfacial polarization induced by the large number of interfaces.
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Fig.5 (c) and (d) show the similar frequency dispersions of relative complex permeability ( = − ) for the four measured composite samples. For all the samples, the real part of
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relative permeability ( ) is about 2-2.3 at 1 GHz and then decreases rapidly to ~1 at 18 GHz. The imaginary part ( ) curve shows fluctuation between 0.2 and 0.7. As the size effect is concerned, the nano-sized particles have a little higher value than the micro-sized ones for
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either Fe or Fe4N. This is consistent with the hysteresis loop results in Fig.4, showing a larger saturation magnetization by the nano-sized particles. Comparing the curves of of the four samples, a sharp resonance peak can be seen at
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13.5 GHz for the composite with micro-sized Fe4N particles, while, a broad resonance maximum
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exists at ~6 GHz for the one with nano-sized Fe4N particles. The resonance phenomenon is not distinguishable for those with Fe particles. The ferromagnetic resonance is believed to be beneficial for magnetic loss and contributed for the microwave absorption abilities. It is well known that the ferromagnetic resonance frequency (fr) is related to its anisotropy fields (Ha) by the following relation [19]: f = γH /2π
(1)
= 2 /
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where γ is the gyromagnetic ratio, K1 is the first anisotropic coefficient, µ o is permeability of vacuum. From the above formula, the lower resonance frequency of nano-sized Fe4N particles is
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due to the smaller anisotropy field or the higher Ms than the micro-sized ones. The result is also consistent with the hysteresis loop in Fig.4.
Based on the measured permittivity and permeability, the reflection loss (RL) curves were
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calculated according to the following equations: RL = 20log|( − 1)/( + 1)| /)
'&
tanh [(
)/01 2
3
)( )4 ]
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= $ & (
(3)
(4)
Where Zin is the normalized input impedance at the absorber surface, c is the velocity of light, d is the thickness of absorber, and f is the frequency of incident electromagnetic wave.
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3.3 microwave absorption property analysis
Fig.6 shows the relationship curves between RL and f for the wax composites with 75 wt. % Fe and Fe4N particles. The typical absorbing parameters such as RL, frequency, and the thickness
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of the composite absorbers, obtained from Fig.6 were listed in Table 1. The Fe4N particles
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exhibited much stronger absorption in a lower frequency range than Fe particles. The RL values of less than -10 dB are observed in a wide frequency bandwidth from 1.8 to 11 GHz for nano-sized Fe4N composite with absorber thickness of 1.2-5.0 mm. Its minimum RL value (RLmin = -33 dB) appears at 3.5 GHz with a thickness of 3.0 mm. Compared with nano-sized Fe4N, the RL curves of micro-sized Fe4N showed weaker and higher frequency absorption characteristics. Its RLmin = -29 dB appears at 4.9 GHz with the same thickness. The frequency bandwidth for RL<-10 dB is from 4 to 12.5 GHz with the thickness of 1.5-3.0 mm. From Table 1, 8
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it can be seen that when the thickness is 2.0 mm, the frequency of absorption peak (f2) is 11.5, 8.0, 7.9, and 5.4 GHz for micro-sized Fe, nano-sized Fe, micro-sized Fe4N and nano-sized Fe4N,
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respectively. The results indicated that both the nanometer size and the single-phase Fe4N have remarkable effects on shifting the absorption peaks towards the lower frequency. Furthermore, as listed in Table 2, nano-sized Fe4N exhibits the most excellent absorption properties among all the
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samples in the frequency of 2-8 GHz in comparison to that of the reported Fe nanocomposites
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such as Fe nanospheres [20], Fe nanowires [20] and flake-shaped carbonyl Fe [21]. The microwave absorption properties of these reported composites are listed in Table 2. The different absorption properties can be explained by the different electromagnetic parameters. From Fig.5, the permittivity values of nano-sized magnetic particles are of a higher
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order of magnitude than those of micro-sized one and the permeability values are a little higher in the nano-sized particles than the micro-sized ones. Therefore, the size effect on the microwave absorbing characteristics was depended on both the dielectric and the magnetic properties of
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these composites. The moderate larger permittivity and permeability, especially the higher of
range.
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the nano-sized particles contribute for the blue shift of absorbing frequency in the 1-18 GHz
From the frequency dependence of the relative permittivity for the wax composites with Fe particles (no matter of micro-size or nano-size), one can observe that no dielectric resonance peak is present in the range of 1-18 GHz. However, obvious dielectric resonance peaks can be observed around 12-16 GHz in and curves of the composites with Fe4N particles (no matter of micro-size or nano-size). The above experimental results suggested that single-phase 9
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Fe4N particles have significant dielectric resonance effect which is one of the main reasons for the strong absorption in the range of 2-8 GHz. Besides, for the same particle size, Fe4N has
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higher magnetic loss than Fe, as shown in Fig.7, especially in the lower frequency range from 1 to 8 GHz. For nano-sized Fe4N composites, the magnetic loss tanδm is higher than electric loss tanδe, indicating that magnetic loss other than electric loss plays a key role on the microwave
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absorption mechanism.
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4. Conclusions
Single-phase Fe4N particles of nano- and micro-size were prepared by an economical and large-scale gaseous nitriding method. The microwave absorbing properties of wax composites with Fe4N and Fe particles of the same size scale were compared over the range of 1-18 GHz.
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The results indicated that nano-sized particles had superior absorbing performance at lower frequency band than the corresponding micro-sized ones. Among the four examined absorbers, the nano-sized Fe4N particles are the best candidate for microwave absorption at S and C bands.
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The RL values of less than -10 dB are observed in a wide frequency bandwidth from 1.8 to 11
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GHz for nano-sized Fe4N composite with the absorber thickness of 1.2-5.0 mm. Its minimum RL value (RLmin = -33 dB) appears at 3.5 GHz with a thickness of 3.0 mm. The nanosize effect on the microwave absorbing characteristics was depended on both the dielectric and the magnetic property. The higher dielectric constant of nano-sized particles than micro-sized ones mainly due to the interfacial polarization induced by the large number of interfaces. While, the dielectric resonance effect is the main reasons for the strong absorption of Fe4N at lower frequency than Fe particles. 10
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As far as we know, the nano-sized Fe4N particles is the firstly reported absorber whose reflection loss reaches -16 dB at 2 GHz with the thickness of as thin as 5 mm. The wax
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composites with the nano-sized Fe4N particles showed good microwave absorbing characteristics at S and C bands (2-8 GHz). This study demonstrated the possible application of producing thin
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and light absorbers from the nano-sized Fe4N particles.
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Acknowledgment
This work is financially supported by Ministry of Science and Technology of the People's Republic of China (Grant No. 2011CB605601). References
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[1] Y. Yang, Y. Yang, W. X, J. Ding, Microwave electromagnetic and absorption properties of magnetite hollow nanostructures, J. Appl. Phys. 115 (2014) 17A521-1-3. [2] Y. B. Feng T. Qiu, Preparation, characterization and microwave absorbing properties of FeNi
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alloy prepared by gas atomization method, J. Alloys. Compd. 513 (2012) 455-459.
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[3] S. J. Yan, L. Zhen, C. Y. Xu, J. T. Jiang, W. Z. Shao, Microwave absorption properties of FeNi3 submicrometre spheres and SiO2@FeNi3core–shell structures, J. Phys. D: Appl. Phys. 43 (2010) 245003-1-7.
[4] M. G. Han, W. Tang, W. B. Chen, H. Zhou, L. J. Deng, Effect of shape of Fe particles on their electromagnetic properties within 1–18 GHz range, J. Appl. Phys. 107 (2010) 09A958-1-3. [5] D. L. Huber, Synthesis, Properties, and applications of iron nanoparticles, Small 1 (2005) 482-501. 11
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[6] Y. J. Shi, Y. L. Du, G. Chen, Ab initio study of structural and magnetic properties of cubic Fe4N (0 01) surface, Solid State Commun. 152 (2012) 1581-1584.
ε-Fe3N particles, J. Alloys. Compd. 443 (2007) 48-52.
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[7] W. Huang, J. Wu, W. Guo, R. Li, L. Cui, Preparation and magnetic properties of nanoscale
[8] L. Rissanen, M. Neubauer, K. P. Lieb, P. Schaaf, The new cubic iron-nitride phase FeN
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prepared by reactive magnetron sputtering, J. Alloys. Compd. 274 (1998) 74-82.
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[9] S. Kokado, N. Fujima, K. Harigaya, H. Shimizu, A. Sakuma, Theoretical analysis of highly spin-polarized transport in the iron nitride Fe4N, Pys. Rev. B 73 (2006) 172410-1-2. [10] X. Bao, R. M. Metzger, W. D. Doyle, Synthesis of high moment and high coercivity iron nitride particles, J. Appl. Phys. 73 (1993) 6734-6736.
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[11] L.L. Wang, W.T. Zheng, J. Gong, H.B. Li, X. Wang, N. Ma, P.J. Cao, X.C. Ma, Investigation on the structure and magnetic properties at low temperature for nanocrystalline -Fe4N thin films, J. Alloys. Compd. 467 (2009) 1-5.
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[12] X. L. Wu, W. Zhong, H. Y. Jiang, N. J. Tang, W. Q. Zou, Y. W. Du, Magnetic properties and
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thermal stability of γ’-Fe4N nanoparticles prepared by a combined method of reduction and nitriding, J. Magn. Magn. Mater. 281 (2004) 77-81. [13] Y. R. Jang, I. G. Kim, J. I. Lee, Electronic structure and magnetic properties of Fe4N (001), J. Magn. Magn. Mater. 263 (2003) 366-327. [14] S. K. Chen, S. Jin, T. H. Tiefei, Y. F. Hsieh, E. M. Gyorgy, D. E. Johnson, Magnetic properties and microstructure of Fe4N and (Fe,Ni)4N, J. Appl. Phys. 70 (1991) 6247-6249. [15] D. Moszyński, I. Moszyńska, W. Arabzyk, The transformation of α-Fe into γ′-Fe4N in 12
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nanocrystalline Fe–N system: Influence of Gibbs–Thomson effect, Appl. Phys. Lett. 103 (2013) 253108-1-4.
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[16] T. Yamaguchi, M. Sakita, M. Nakamura, T. Kobira, Synthesis and characteristics of Fe4N powders and thin films, J. Magn. Magn. Mater. 215-216 (2000) 529-531.
[17] T. Hyeon, Chemical synthesis of magnetic nanoparticles, Chem Commun. 4 (2003)
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927-934.
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[18] L. Reichel, G. Giannopoulos, S. Kauffmann-Weiss, M. Hoffmann, D. Pohl, A. Edstrom, S. Oswald, D. Niarchos, J. Rusz, L. Schultz, S. Fahler, Increased magnetocrystalline anisotropy in epitaxial Fe-Co-C thin films with spontaneous strain, J. Appl. Phys. 116 (2014) 213901-1-7.
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[19] S. B. Liao, Physics of Ferromagnetism, the second volum, Science, Beijing, 1998. [20] X. H. Li, X. H. Guo, T. C. Liu, X. L. Zheng, J. T. Bai, Shape-controlled synthesis of Fe nanostructures and their enhanced microwave absorption properties at L-band, Mater. Res. Bull.
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59 (2014) 137-141.
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[21] T. Wang, R. Han, G. Tan, J. Q. Wei, L. Qiao, F. S. Li, Reflection loss mechanism of single layer absorber for flake-shaped carbonyl-iron particle composite, J. Appl. Phys. 112 (2012) 104903-1-6.
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Table 1 Characteristic parameters of RL-f curves in Fig.6 Bandwidth (GHz)
RLmin
f (GHz)
d (mm)
particles
for RL<-10 dB
(dB)
for RLmin
for RLmin
d = 2.0 mm
d = 2.0 mm
micro-Fe
5.9-18.0
-33
16.6
1.5
-25.0
11.5
nano-Fe
4.4-14.4
-27
6.3
2.5
-26.6
8.0
micro-Fe4N
4.0-12.4
-29
4.9
3.0
-15
7.9
nano-Fe4N
3.0-8.8
-33
-18
5.4
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Table 2
RL (dB) for
3.5
3.0
f2 (GHz) for
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Magnetic
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Microwave absorption properties of some reported composites and nano-sized Fe4N particles Bandwidth Magnetic
(GHz) for
RLmin
f (GHz)
d (mm) for Reference
d (mm)
RL<-10
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particles
(dB)
for RLmin
RLmin
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dB
Fe nanospheres
0.9-3.7
1.5-6.0
-33
1.3
5
20
Fe nanowires
0.8-2.1
2.0-4.0
-32
1.1
3.5
20
3.7-12
1.2-6.4
-35
4.6
2.3
21
1.8-11
1.2-5.0
-33
3.5
3.0
This work
Flake-shaped carbonyl Fe nano-Fe4N
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Figure captions:
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Fig.1. SEM images of micro-sized Fe particles (a), (b) before nitriding and (c), (d) after nitriding. Fig.2. SEM images of nano-sized Fe particles (a), (b) before nitriding and (c), (d) after nitriding. Fig.3. XRD patterns of nano-sized and micro-sized Fe particles before and after nitriding.
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Fig.4. Hysteresis loops at 293K of Fe4N particles of different sizes.
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Fig.5. (a), (b) The relative complex permittivity and (c), (d) the relative complex permeability of the wax composites with 75 wt. % Fe or Fe4N particles of different sizes. Fig.6. Frequency dependency of RL of the wax composites with 75 wt.% magnetic Fe4N particles: (a) micro-sized Fe (b) nano-sized Fe (c) micro-sized Fe4N (d) nano-sized Fe4N.
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Fig.7. Electric and magnetic loss tangent of the wax composites with 75 wt. % magnetic particles
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of (a) nano-size and (b) micro-size.
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ACCEPTED MANUSCRIPT Nano- and micro-sized single-phase Fe4N particles were prepared by nitriding.
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Size and phase effects on the microwave absorption properties were discussed.
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Nano-sized particles had superior absorbing performance at lower frequency band.
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The minimum RL value (-33 dB) of nano-sized Fe4N appears at 3.5 GHz with d=3.0 mm.
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The bandwidth of RL<-10 dB covers the whole S and C bands with thin thickness.
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S0925-8388(15)31261-5
DOI:
10.1016/j.jallcom.2015.10.005
Reference:
JALCOM 35560
To appear in:
Journal of Alloys and Compounds
Received Date: 7 April 2015 Revised Date:
1 July 2015
Accepted Date: 1 October 2015
Please cite this article as: M. Yu, Y. Xu, Q. Mao, F. Li, C. Wang, Electromagnetic and absorption properties of nano-sized and micro-sized Fe4N particles, Journal of Alloys and Compounds (2015), doi: 10.1016/j.jallcom.2015.10.005. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Electromagnetic and absorption properties of nano-sized and micro-sized Fe4N particles Meijie Yu a, *, Yong Xu b, Qiong Mao a, Fazhan Li a, Chengguo Wang a, * College of Materials Science and Engineering, Shandong University, Jinan 250061, People’s
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a
Republic of China b
College of Materials Science and Engineering, Shandong Jianzhu University, Jinan 250101,
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People’s Republic of China
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ABSTRACT:
Single-phase Fe4N has been synthesized by gaseous nitriding micro-sized and nano-sized Fe particles at 793K under ammonia atmosphere. The electromagnetic properties of their wax composite with 75 wt. % magnetic particles have been investigated within the frequency range of
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1–18 GHz. Both size and phase effects on the microwave absorption properties were discussed on the results of scanning electronic microscopy, X-ray diffraction, hysteresis loop, and the frequency dependence of complex permittivity and permeability. The results show that
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nano-sized particles have superior absorbing performance at lower frequency band than the
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corresponding micro-sized ones, which is mainly attributed to the higher dielectric constant caused by interfacial polarization. The Fe4N composites exhibit much stronger absorption in 2–8 GHz than Fe composites. The reflection loss (RL) values of less than -10 dB are observed in a wide frequency bandwidth from 1.8 to 11 GHz for nano-sized Fe4N composite with absorber
*
Corresponding author at: College of Materials Science and Engineering, Shandong University, Jinan 250061, People’s Republic of China. (Meijie Yu) Tel: +86-531-88396181 E-mail address: [email protected] (Meijie Yu); [email protected] (Chengguo Wang)
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thickness of 1.2–5.0 mm. Its minimum RL value (RLmin = -33 dB) appears at 3.5 GHz with a thickness of 3.0 mm. This study demonstrates the possible application of producing thin and light
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absorbers from nano-sized Fe4N particles for microwave absorption at S and C bands (2–8 GHz). Keywords: iron nitride; nanoparticle; electromagnetic property; X-ray diffraction 1. Introduction
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Microwave electromagnetic and absorption property of magnetic nanoparticles is a topic of
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interest due to the rapid development of wireless communication, ultrafast high density data storage and the military purpose in radar absorption [1]. Compared with the commonly used ferrites, ferromagnetic metal-based nanomaterials are promised to be more suitable as microwave absorbers with thin thickness and wider working frequency owing to their larger saturation
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magnetization and higher Snoek’s limit at high frequency [2-4]. As an important ferromagnetic metal, iron (α-Fe) has been widely used as a candidate for microwave absorption applications because of low magneto-crystalline anisotropy, high Curie temperatures (Tc = 1043K), and the
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highest room-temperature saturation magnetization (Ms = 218 emu/g) of any ferromagnetic
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elements [5]. Nevertheless, the greatest weakness of iron is its reactivity, especially with respect to water and oxygen. This general weakness is greatly multiplied in the case of iron nanoparticles, where the iron rapidly and completely oxidized in air. Recently, iron nitrides have received much attention by virtue of the excellent magnetic properties, low coercivity in combination with significantly improved corrosion resistance over pure iron [6-8]. Among the ferromagnetic nitrides, γ’ phase of iron nitride (Fe4N) is of special interest. This nitride has a perovskite-type structure, in which N is located at the body center 2
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position of fcc-Fe [9]. Due to its large saturation magnetization [10], lower coercive force [11], and chemical stability [12], the Fe4N has been considered as an important material in the fields
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of ferrofluids, high density magnetic recording, and magnetic refrigeration. Considerable studies have been done theoretically and experimentally on the electronic structure and magnetic
properties of Fe4N [13, 14]. However the microwave absorption properties of nanoparticle Fe4N
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in the 2-18 GHz frequency range have seldom been reported to date. Moreover, the
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ferromagnetic particles and their composites used as microwave absorbers often possess a size of micrometer or nanometer. The relationship between the electromagnetic properties and the size effect has not been well understood.
In this paper, we demonstrate excellent microwave absorption by single-phase Fe4N
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nanoparticles over broad frequency range. For the thickness of the absorbers between 1.5 and 3mm, the reflection loss (RL) values less than -10 dB are obtained in a range of 2-8 GHz, which covers the whole S band (2-4 GHz) and C band (4-8 GHz). The size and phase effects on the
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electromagnetic and absorption properties of Fe4N and Fe particles have been analyzed in detail.
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2. Experimental procedure
The starting materials to prepare Fe4N particles were the commercial micro-sized carbonyl iron powder with 99.5 % purity and the nano-sized pure iron powder without any surface treatment. Fe4N particles were prepared by gaseous nitriding method. The iron particles of micro-size and nano-size were heat treated under the same nitriding conditions: temperature 793 K, the ammonia decomposition rate ~68 %, heat treatment time 5 h. From room temperature to 793 K, nitrogen was used to protect the materials from oxidation; up to 793 K, nitrogen was 3
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substituted by ammonia. For the aim of preventing oxidation and aggregation, the nano-sized Fe particles were coated with polyvinylpyrrolidone (PVP) in our laboratory before gaseous nitriding.
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In a typical process, 10 g Fe nanoparticles, isolated with air, were added into PVP aqueous solution (0.02 g/ml) and mechanical stirred for 20 min. The coated Fe nanoparticles were precipitated by magnet, washed with alcohol and then dried in vacuum.
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The X-ray powder diffraction data was collected in 2θ range of 10-90° using a Bruker AXS
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D8 advanced diffractometer with Cu Kα radiation under 40 kV and 50 mA. The morphology of the magnetic particles was observed by a field emission scanning electron microscopy (FESEM, SU-70). Static magnetic measurement was carried out on a vibrating sample magnetometer (VSM, JDAW-2000＆D) at room temperature with an applied field up to 10 kOe. For microwave
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absorption measurements, the samples were the wax composite with 75 wt. % magnetic particles, which were made into toroidal shape with an outer diameter of 7.00 mm and an inner diameter of 3.04 mm. The complex permeability and permittivity over 1-18 GHz were calculated from the
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S-parameters measured using a vector network analyzer (VNA, HP 8722ES) with a
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transmission-reflection-line (TRL) calibration. 3. Results and discussion
3.1 SEM and XRD analysis
Fig.1 shows the SEM morphologies of the micro-sized Fe particles before and after nitriding treatment. The diameter (1-4 µm) keeps almost unchanged, while the shape becomes slightly irregular after nitriding treatment. Meanwhile, the surface morphology of the particles changes from smooth to coarse. Compared with the micro-sized particles, more obvious changes 4
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can be observed in nano-sized ones as shown in Fig.2. After nitriding treatment, the nano-sized Fe particles lost their spherical appearance, becoming more irregular with lamellar texture.
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The XRD patterns (Fig.3) confirm that the phase compositions change from α-Fe to single-phase γ’-Fe4N for both the micro- and nano-sized particles after nitriding under the certain conditions. We found that the phase composition was strongly dependent on the ammonia
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decomposition rate. In order to obtain single-phase Fe4N, the ammonia decomposition rate must
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be confined in a much narrower range for nano-sized particles than the micro-sized ones. Mixed phases of α-Fe and γ’-Fe4N were observed for the nano-sized particles when decreasing the ammonia decomposition rate from ~68 %. This behavior is presumably a result of Gibbs-Thomson effect [15]. The grain size estimated by Scherrer’s formula is 30-40 nm and
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40-50 nm for the nano-sized and micro-sized Fe4N particles, respectively. 3.2 Electromagnetic properties analysis
Fig.4 shows the hysteresis loops of the Fe4N particles of the two different sizes, which
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exhibit that both samples have excellent soft magnetic properties. The Ms value of micro-sized
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Fe4N particles is 196 emu/g, which is a little higher than the value (188 ± 2 emu/g) reported previously [16]. The Ms value of nano-sized Fe4N particles is 221 emu/g, which is higher than not only that of micro-sized Fe4N particles in the present study, but also the reported sheet-form Fe4N (179 emu/g) [14] and pure iron (218 emu/g) [15]. Moreover, the approach of nano-sized particles to saturation occurs at a much smaller field. It means that their static permeability is higher than that of relatively larger particles. This is confirmed by the following results in Fig.5 (d). Meanwhile, the nano-sized Fe4N particles demonstrate higher coercivity (Hc, 118 Oe) than 5
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that of the micro-sized Fe4N (38 Oe). Generally, the Hc of magnetic nanoparticles is mainly composed by crystalline anisotropy and shape anisotropy [17]. Typically, due to symmetry
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reasons, the magneto-crystalline anisotropy is much weaker in cubic materials [18]. As confirmed by XRD results, both the Fe4N particles have nano-sized crystals of fcc structure, implying that the crystalline anisotropies of the Fe4N particles of different sizes are almost the
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same. Therefore, the difference in Hc can be attributed to the shape anisotropy. The nano-sized
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Fe4N particles possess much stronger shape anisotropy than the micro-sized ones thus resulting in higher Hc.
Fig.5 (a) and (b) show the frequency dependence of the relative complex permittivity ( = − ) for the wax composites with 75 wt. % Fe or Fe4N particles. For the wax composites with the micro-sized Fe particles, the real part and the imaginary part of relative
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permittivity keep almost constant ( = ~7.5 and = ~0.1) with increasing frequency from 1 to 18 GHz. The similar characteristics was also observed for the composites with nano-sized Fe
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particles. The and values slightly decline with increasing frequency from 15.7 and 4.1 to
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13.4 and 2.7 in 1-4 GHz, and keep almost constant ( = ~13 and = ~2.2) between 4 and 18 GHz. Comparing with the micro-sized Fe particles, the nano-sized Fe particles exhibited a higher permittivity level, which can be attributed to the increase of space-charge polarization between nano-sized Fe particles isolated by PVP, more efficiently after mixing with wax homogeneously. Compared with Fig.5 (a), Fig.5 (b) exhibits obvious differences in and curves. Dielectric resonance peaks were observed at 12.5 and 14.4 GHz for the composites with Fe4N particles of micro-size and nano-size, respectively; while no dielectric resonance peak was found for the 6
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composites with Fe particles. This result indicates Fe4N particles possess different polarization mode with Fe particles. From Fig.5 (b), the composite with nano-sized Fe4N particles also have a
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higher than that with micro-sized ones. Therefore, either for Fe or Fe4N, the higher dielectric constant of nano-sized particles than micro-sized ones mainly due to the interfacial polarization induced by the large number of interfaces.
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Fig.5 (c) and (d) show the similar frequency dispersions of relative complex permeability ( = − ) for the four measured composite samples. For all the samples, the real part of
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relative permeability ( ) is about 2-2.3 at 1 GHz and then decreases rapidly to ~1 at 18 GHz. The imaginary part ( ) curve shows fluctuation between 0.2 and 0.7. As the size effect is concerned, the nano-sized particles have a little higher value than the micro-sized ones for
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either Fe or Fe4N. This is consistent with the hysteresis loop results in Fig.4, showing a larger saturation magnetization by the nano-sized particles. Comparing the curves of of the four samples, a sharp resonance peak can be seen at
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13.5 GHz for the composite with micro-sized Fe4N particles, while, a broad resonance maximum
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exists at ~6 GHz for the one with nano-sized Fe4N particles. The resonance phenomenon is not distinguishable for those with Fe particles. The ferromagnetic resonance is believed to be beneficial for magnetic loss and contributed for the microwave absorption abilities. It is well known that the ferromagnetic resonance frequency (fr) is related to its anisotropy fields (Ha) by the following relation [19]: f = γH /2π
(1)
= 2 /
(2) 7
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where γ is the gyromagnetic ratio, K1 is the first anisotropic coefficient, µ o is permeability of vacuum. From the above formula, the lower resonance frequency of nano-sized Fe4N particles is
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due to the smaller anisotropy field or the higher Ms than the micro-sized ones. The result is also consistent with the hysteresis loop in Fig.4.
Based on the measured permittivity and permeability, the reflection loss (RL) curves were
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calculated according to the following equations: RL = 20log|( − 1)/( + 1)| /)
'&
tanh [(
)/01 2
3
)( )4 ]
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%
= $ & (
(3)
(4)
Where Zin is the normalized input impedance at the absorber surface, c is the velocity of light, d is the thickness of absorber, and f is the frequency of incident electromagnetic wave.
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3.3 microwave absorption property analysis
Fig.6 shows the relationship curves between RL and f for the wax composites with 75 wt. % Fe and Fe4N particles. The typical absorbing parameters such as RL, frequency, and the thickness
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of the composite absorbers, obtained from Fig.6 were listed in Table 1. The Fe4N particles
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exhibited much stronger absorption in a lower frequency range than Fe particles. The RL values of less than -10 dB are observed in a wide frequency bandwidth from 1.8 to 11 GHz for nano-sized Fe4N composite with absorber thickness of 1.2-5.0 mm. Its minimum RL value (RLmin = -33 dB) appears at 3.5 GHz with a thickness of 3.0 mm. Compared with nano-sized Fe4N, the RL curves of micro-sized Fe4N showed weaker and higher frequency absorption characteristics. Its RLmin = -29 dB appears at 4.9 GHz with the same thickness. The frequency bandwidth for RL<-10 dB is from 4 to 12.5 GHz with the thickness of 1.5-3.0 mm. From Table 1, 8
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it can be seen that when the thickness is 2.0 mm, the frequency of absorption peak (f2) is 11.5, 8.0, 7.9, and 5.4 GHz for micro-sized Fe, nano-sized Fe, micro-sized Fe4N and nano-sized Fe4N,
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respectively. The results indicated that both the nanometer size and the single-phase Fe4N have remarkable effects on shifting the absorption peaks towards the lower frequency. Furthermore, as listed in Table 2, nano-sized Fe4N exhibits the most excellent absorption properties among all the
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samples in the frequency of 2-8 GHz in comparison to that of the reported Fe nanocomposites
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such as Fe nanospheres [20], Fe nanowires [20] and flake-shaped carbonyl Fe [21]. The microwave absorption properties of these reported composites are listed in Table 2. The different absorption properties can be explained by the different electromagnetic parameters. From Fig.5, the permittivity values of nano-sized magnetic particles are of a higher
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order of magnitude than those of micro-sized one and the permeability values are a little higher in the nano-sized particles than the micro-sized ones. Therefore, the size effect on the microwave absorbing characteristics was depended on both the dielectric and the magnetic properties of
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these composites. The moderate larger permittivity and permeability, especially the higher of
range.
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the nano-sized particles contribute for the blue shift of absorbing frequency in the 1-18 GHz
From the frequency dependence of the relative permittivity for the wax composites with Fe particles (no matter of micro-size or nano-size), one can observe that no dielectric resonance peak is present in the range of 1-18 GHz. However, obvious dielectric resonance peaks can be observed around 12-16 GHz in and curves of the composites with Fe4N particles (no matter of micro-size or nano-size). The above experimental results suggested that single-phase 9
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Fe4N particles have significant dielectric resonance effect which is one of the main reasons for the strong absorption in the range of 2-8 GHz. Besides, for the same particle size, Fe4N has
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higher magnetic loss than Fe, as shown in Fig.7, especially in the lower frequency range from 1 to 8 GHz. For nano-sized Fe4N composites, the magnetic loss tanδm is higher than electric loss tanδe, indicating that magnetic loss other than electric loss plays a key role on the microwave
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absorption mechanism.
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4. Conclusions
Single-phase Fe4N particles of nano- and micro-size were prepared by an economical and large-scale gaseous nitriding method. The microwave absorbing properties of wax composites with Fe4N and Fe particles of the same size scale were compared over the range of 1-18 GHz.
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The results indicated that nano-sized particles had superior absorbing performance at lower frequency band than the corresponding micro-sized ones. Among the four examined absorbers, the nano-sized Fe4N particles are the best candidate for microwave absorption at S and C bands.
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The RL values of less than -10 dB are observed in a wide frequency bandwidth from 1.8 to 11
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GHz for nano-sized Fe4N composite with the absorber thickness of 1.2-5.0 mm. Its minimum RL value (RLmin = -33 dB) appears at 3.5 GHz with a thickness of 3.0 mm. The nanosize effect on the microwave absorbing characteristics was depended on both the dielectric and the magnetic property. The higher dielectric constant of nano-sized particles than micro-sized ones mainly due to the interfacial polarization induced by the large number of interfaces. While, the dielectric resonance effect is the main reasons for the strong absorption of Fe4N at lower frequency than Fe particles. 10
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As far as we know, the nano-sized Fe4N particles is the firstly reported absorber whose reflection loss reaches -16 dB at 2 GHz with the thickness of as thin as 5 mm. The wax
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composites with the nano-sized Fe4N particles showed good microwave absorbing characteristics at S and C bands (2-8 GHz). This study demonstrated the possible application of producing thin
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and light absorbers from the nano-sized Fe4N particles.
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Acknowledgment
This work is financially supported by Ministry of Science and Technology of the People's Republic of China (Grant No. 2011CB605601). References
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[1] Y. Yang, Y. Yang, W. X, J. Ding, Microwave electromagnetic and absorption properties of magnetite hollow nanostructures, J. Appl. Phys. 115 (2014) 17A521-1-3. [2] Y. B. Feng T. Qiu, Preparation, characterization and microwave absorbing properties of FeNi
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alloy prepared by gas atomization method, J. Alloys. Compd. 513 (2012) 455-459.
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[3] S. J. Yan, L. Zhen, C. Y. Xu, J. T. Jiang, W. Z. Shao, Microwave absorption properties of FeNi3 submicrometre spheres and SiO2@FeNi3core–shell structures, J. Phys. D: Appl. Phys. 43 (2010) 245003-1-7.
[4] M. G. Han, W. Tang, W. B. Chen, H. Zhou, L. J. Deng, Effect of shape of Fe particles on their electromagnetic properties within 1–18 GHz range, J. Appl. Phys. 107 (2010) 09A958-1-3. [5] D. L. Huber, Synthesis, Properties, and applications of iron nanoparticles, Small 1 (2005) 482-501. 11
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[6] Y. J. Shi, Y. L. Du, G. Chen, Ab initio study of structural and magnetic properties of cubic Fe4N (0 01) surface, Solid State Commun. 152 (2012) 1581-1584.
ε-Fe3N particles, J. Alloys. Compd. 443 (2007) 48-52.
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[7] W. Huang, J. Wu, W. Guo, R. Li, L. Cui, Preparation and magnetic properties of nanoscale
[8] L. Rissanen, M. Neubauer, K. P. Lieb, P. Schaaf, The new cubic iron-nitride phase FeN
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prepared by reactive magnetron sputtering, J. Alloys. Compd. 274 (1998) 74-82.
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[9] S. Kokado, N. Fujima, K. Harigaya, H. Shimizu, A. Sakuma, Theoretical analysis of highly spin-polarized transport in the iron nitride Fe4N, Pys. Rev. B 73 (2006) 172410-1-2. [10] X. Bao, R. M. Metzger, W. D. Doyle, Synthesis of high moment and high coercivity iron nitride particles, J. Appl. Phys. 73 (1993) 6734-6736.
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[11] L.L. Wang, W.T. Zheng, J. Gong, H.B. Li, X. Wang, N. Ma, P.J. Cao, X.C. Ma, Investigation on the structure and magnetic properties at low temperature for nanocrystalline -Fe4N thin films, J. Alloys. Compd. 467 (2009) 1-5.
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[12] X. L. Wu, W. Zhong, H. Y. Jiang, N. J. Tang, W. Q. Zou, Y. W. Du, Magnetic properties and
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thermal stability of γ’-Fe4N nanoparticles prepared by a combined method of reduction and nitriding, J. Magn. Magn. Mater. 281 (2004) 77-81. [13] Y. R. Jang, I. G. Kim, J. I. Lee, Electronic structure and magnetic properties of Fe4N (001), J. Magn. Magn. Mater. 263 (2003) 366-327. [14] S. K. Chen, S. Jin, T. H. Tiefei, Y. F. Hsieh, E. M. Gyorgy, D. E. Johnson, Magnetic properties and microstructure of Fe4N and (Fe,Ni)4N, J. Appl. Phys. 70 (1991) 6247-6249. [15] D. Moszyński, I. Moszyńska, W. Arabzyk, The transformation of α-Fe into γ′-Fe4N in 12
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nanocrystalline Fe–N system: Influence of Gibbs–Thomson effect, Appl. Phys. Lett. 103 (2013) 253108-1-4.
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[16] T. Yamaguchi, M. Sakita, M. Nakamura, T. Kobira, Synthesis and characteristics of Fe4N powders and thin films, J. Magn. Magn. Mater. 215-216 (2000) 529-531.
[17] T. Hyeon, Chemical synthesis of magnetic nanoparticles, Chem Commun. 4 (2003)
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927-934.
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[18] L. Reichel, G. Giannopoulos, S. Kauffmann-Weiss, M. Hoffmann, D. Pohl, A. Edstrom, S. Oswald, D. Niarchos, J. Rusz, L. Schultz, S. Fahler, Increased magnetocrystalline anisotropy in epitaxial Fe-Co-C thin films with spontaneous strain, J. Appl. Phys. 116 (2014) 213901-1-7.
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[19] S. B. Liao, Physics of Ferromagnetism, the second volum, Science, Beijing, 1998. [20] X. H. Li, X. H. Guo, T. C. Liu, X. L. Zheng, J. T. Bai, Shape-controlled synthesis of Fe nanostructures and their enhanced microwave absorption properties at L-band, Mater. Res. Bull.
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59 (2014) 137-141.
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[21] T. Wang, R. Han, G. Tan, J. Q. Wei, L. Qiao, F. S. Li, Reflection loss mechanism of single layer absorber for flake-shaped carbonyl-iron particle composite, J. Appl. Phys. 112 (2012) 104903-1-6.
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Table 1 Characteristic parameters of RL-f curves in Fig.6 Bandwidth (GHz)
RLmin
f (GHz)
d (mm)
particles
for RL<-10 dB
(dB)
for RLmin
for RLmin
d = 2.0 mm
d = 2.0 mm
micro-Fe
5.9-18.0
-33
16.6
1.5
-25.0
11.5
nano-Fe
4.4-14.4
-27
6.3
2.5
-26.6
8.0
micro-Fe4N
4.0-12.4
-29
4.9
3.0
-15
7.9
nano-Fe4N
3.0-8.8
-33
-18
5.4
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Table 2
RL (dB) for
3.5
3.0
f2 (GHz) for
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Magnetic
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Microwave absorption properties of some reported composites and nano-sized Fe4N particles Bandwidth Magnetic
(GHz) for
RLmin
f (GHz)
d (mm) for Reference
d (mm)
RL<-10
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particles
(dB)
for RLmin
RLmin
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dB
Fe nanospheres
0.9-3.7
1.5-6.0
-33
1.3
5
20
Fe nanowires
0.8-2.1
2.0-4.0
-32
1.1
3.5
20
3.7-12
1.2-6.4
-35
4.6
2.3
21
1.8-11
1.2-5.0
-33
3.5
3.0
This work
Flake-shaped carbonyl Fe nano-Fe4N
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Figure captions:
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Fig.1. SEM images of micro-sized Fe particles (a), (b) before nitriding and (c), (d) after nitriding. Fig.2. SEM images of nano-sized Fe particles (a), (b) before nitriding and (c), (d) after nitriding. Fig.3. XRD patterns of nano-sized and micro-sized Fe particles before and after nitriding.
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Fig.4. Hysteresis loops at 293K of Fe4N particles of different sizes.
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Fig.5. (a), (b) The relative complex permittivity and (c), (d) the relative complex permeability of the wax composites with 75 wt. % Fe or Fe4N particles of different sizes. Fig.6. Frequency dependency of RL of the wax composites with 75 wt.% magnetic Fe4N particles: (a) micro-sized Fe (b) nano-sized Fe (c) micro-sized Fe4N (d) nano-sized Fe4N.
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Fig.7. Electric and magnetic loss tangent of the wax composites with 75 wt. % magnetic particles
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of (a) nano-size and (b) micro-size.
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ACCEPTED MANUSCRIPT Nano- and micro-sized single-phase Fe4N particles were prepared by nitriding.
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Size and phase effects on the microwave absorption properties were discussed.
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Nano-sized particles had superior absorbing performance at lower frequency band.
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The minimum RL value (-33 dB) of nano-sized Fe4N appears at 3.5 GHz with d=3.0 mm.
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The bandwidth of RL<-10 dB covers the whole S and C bands with thin thickness.
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